Semiconductor integrated circuit device and method of manufacturing the same

ABSTRACT

Disclosed is a semiconductor integrated circuit device (e.g., an SRAM) having memory cells each of a flip-flop circuit constituted by a pair of drive MISFETs and a pair of load MISFETs, the MISFETs being cross-connected by a pair of local wiring lines, and having transfer MISFETs, wherein gate electrodes of all of the MISFETs are provided in a first level conductive layer, and the pair of local wiring lines are provided respectively in second and third level conductive layers. The local wiring lines can overlap and have a dielectric therebetween so as to form a capacitance element, to increase alpha particle soft error resistance. Moreover, by providing the pair of local wiring lines respectively in different levels, integration of the device can be increased. Side wall spacers can be provided on the sides of the gate electrodes of the MISFETs and on the sides of the local wiring lines, and connection holes to semiconductor regions of these MISFETs are self-aligned to both the gate electrodes and the local wiring lines, whereby capacitor area can be increased and integration of the device can also be increased.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor integrated circuitdevice and a method for manufacturing the same and, more particularly,to a technique which is particularly effective when applied to asemiconductor integrated circuit device having an SRAM (Static RandomAccess Memory).

A memory cell of an SRAM or a semiconductor memory device is composedof: a flip-flop circuit acting as an information storage unit forstoring information of 1 bit; and a pair of transfer MISFETs (MetalInsulator Semiconductor Field Effect Transistors) for controlling theelectrical connection between writing/reading data lines and theflip-flop circuit.

The flip-flop circuit of the memory cell is composed of a pair of CMOS(Complementary Metal Oxide Semiconductor) inverters, for example. Eachof these CMOS inverters is composed of one drive MISFET and one loadMISFET. In this case, the memory cell is of a complete CMOS type of acombination of two drive MISFETs, two load MISFETs and two transferMISFETs. Of these MISFETs, the transfer MISFETs and the drive MISFETsare of n-channel type whereas the load MISFETs are of p-channel type.

A pair of input/output terminals of the flip-flop circuit (the CMOSinverter) are cross-connected through a pair of wiring lines called"local wiring lines", for example. Moreover, one of these input/outputterminals is supplied with a power supply voltage (e.g., 3 V) of acircuit through a power supply voltage line whereas the other issupplied with a reference voltage (e.g., 0 V) of the circuit through areference voltage line.

In U.S. Pat. No. 5,523,598, issued Jun. 4, 1996, there is disclosed anSRAM of the complete CMOS type, which is equipped with a pair ofaforementioned local wiring lines. In this SRAM, the gate electrodes ofthe six MISFETs constituting the memory cells, the power supply voltageline connected with one input/output terminal of the flip-flop circuit,the reference voltage line connected with the other input/outputterminal, the pair of local wiring lines, and the data lines connectedwith the drain regions of the transfer MISFETs are individually providedin different conductive layers. In this SRAM, moreover, the local wiringlines and other conductive layers (e.g., the reference voltage line) arearranged to intersect each other so that the reduction in the alphaparticle soft error resistance, which might occur upon theminiaturization of the memory cell size and the lowering of theoperating power supply voltage, is prevented by forming a capacitorelement in the intersection region to increase the storage nodecapacitance of the memory cells.

SUMMARY OF THE INVENTION

Various problems arise in connection with the SRAM disclosed in U.S.Pat. No. 5,523,598. In the SRAM disclosed in the aforementioned U.S.Pat. No. 5,523,598, the gate electrodes of the six MISFETs constitutinga memory cell, the paired local wiring lines, the power supply wiringlines (the power supply voltage line and the reference voltage line),and the data lines are formed in different conductive layers. As aresult, the mask registration allowance when forming the connectionholes in the interlayer insulating film by using a photoresist as themask is increased, resulting in increase of the memory cell size. Whenthe gate electrodes are formed of a conductive film of a first layer,the local wiring lines are formed of a conductive film of a secondlayer, and the power supply lines are formed of a conductive film of athird layer, for example, it is necessary to ensure the registrationallowance for both the gate electrodes and the local wiring lines.

In the SRAM disclosed in the aforementioned U.S. Pat. No. 5,523,598, thepaired local wiring lines are formed of the same conductive film. Thismakes it necessary to arrange the two local wiring lines transversely inthe memory cell, so that the memory cell size is increased.

An object of the present invention is to provide a semiconductorintegrated circuit device (for example, a semiconductor memory such as acomplete CMOS SRAM) having a reduced memory cell size, and a method offabricating such semiconductor device.

Another object of the present invention is to provide a semiconductorintegrated circuit device (e.g., semiconductor memory such as a completeCMOS SRAM) having improved alpha particle soft error resistance, and amethod of fabricating such semiconductor device.

The aforementioned and other objects and novel features of the presentinvention will become apparent from the following description to be madewith reference to the accompanying drawings.

Illustrations of the invention to be disclosed herein will be brieflydescribed in the following. These illustrations are representative ofthe present invention and do not define the scope thereof, the scopebeing defined by the appended claims.

According to the present invention, there is provided a semiconductorintegrated circuit device comprising an SRAM including memory cellshaving a flip-flop circuit composed of a pair of drive MISFETs and apair of load MISFETs, and having a pair of transfer MISFETs, whichdevice is constructed such that the individual gate electrodes of thedrive MISFETs, the load MISFETs and the transfer MISFETs are composed ofa first conductive film formed over a major face of a semiconductorsubstrate; one of the local wiring lines cross-connecting a pair ofinput/output terminals of the flip-flop circuit, is composed of a secondconductive film formed over that first conductive film; and the other ofthe local wiring lines is composed of a third conductive film formedover the second conductive film, and a method of fabricating the device.

The semiconductor integrated circuit device of the present invention isconstructed such that the one and the other of the local wiring linesare so arranged as to have at least partially and vertically overlappingportions, and the one and the other of the local wiring lines and aninsulating film interposed therebetween constitute a capacitor element.

In regard to a method for manufacturing a semiconductor integratedcircuit device, there is provided a method for manufacturing asemiconductor integrated circuit device (e.g., an SRAM) containingmemory cells each having a flip-flop circuit including a pair of driveMISFETs and a pair of load MISFETs, and a pair of transfer MISFETs,comprising the steps of:

(a) preparing (e.g., providing) a semiconductor substrate having a majorface, over which the individual gate electrodes of the drive MISFETs,the load MISFETs and the transfer MISFETs are formed;

(b) forming a pair of local wiring lines cross-connecting a pair ofinput/output terminals of the flip-flop circuit, over the gateelectrodes;

(c) forming side wall spacers on the individual side walls of the gateelectrodes and the local wiring lines; and

(d) forming connection holes reaching the source regions of the driveMISFETs or the load MISFETs by depositing a second insulating film of anetching rate different from (e.g., greater than) that of the firstinsulating film over the local wiring lines, on which the side wallspacers are formed, and by etching the second insulating film. Alsoprovided is the device fabricated by this method.

In regard to a method for manufacturing a semiconductor integratedcircuit device, there is also provided a method for manufacturing asemiconductor integrated circuit device (e.g., an SRAM) containingmemory cells each having a flip-flop circuit composed of a pair of driveMISFETs and a pair of load MISFETs, and a pair of transfer MISFETs,comprising the steps of:

(a) preparing (e.g., providing) a semiconductor substrate having a majorface, over which the individual gate electrodes of the drive MISFETs,the load MISFETs and the transfer MISFETs are formed;

(b) forming one of a pair of local wiring lines cross-connecting a pairof input/output terminals of the flip-flop circuit, over the gateelectrodes;

(c) forming the other of the paired local wiring lines over the localwiring line formed in step (d);

(d) forming side wall spacers on the individual side walls of the gateelectrodes and the one and the other of the local wiring lines, byetching a first insulating film which is deposited over the other of thelocal wiring lines; and

(e) forming connection holes reaching the source regions of the driveMISFETs or the load MISFETs by depositing a second insulating film of anetching rate different from that of the first insulating film over theother of the local wiring lines, on which the side wall spacers areformed, and by etching the second insulating film. Also provided is thedevice fabricating by this method.

According to the means thus far described, the paired local wiring linescross-connecting the input/output terminals of the flip-flop circuit ofthe memory cell are formed in different conductive layers verticallywith respect to the substrate. Therefore the space, required when thepaired local wiring lines are composed of the same conductive film, forarranging the two local wiring lines transversely, can be eliminated,and the local wiring lines can be arranged partially in an overlappingmanner, thereby reducing the area occupied by the memory cell.

According to the means thus far described, the one and the other of thelocal wiring lines are so arranged as to overlap vertically, and acapacitor element is formed of the one and the other of the local wiringlines and an insulating film interposed therebetween, so that thestorage node capacitance of the memory cell can be increased, preventingthe lowering of alpha particle soft error resistance entailed by theminiaturization of the memory cell size and the lowering of theoperation power supply voltage. For example, the capacitor area can beabout half the area of the memory cell, which realizes a thick capacitordielectric. Soft error immunity can be achieved even at a 1.8 V supplyvoltage.

According to the means thus far described, the mask registrationallowance when the connection holes are formed in the interlayerinsulating film by using a photoresist as the mask can be eliminated,reducing the area occupied by the memory cells. The connection holes canbe formed by a self-alignment technique (self-aligned to both the gatesand the local wiring lines).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view showing a memory cell of an SRAM of a firstembodiment according to the present invention.

FIG. 2 is a section of the memory cell taken along line A-A' of FIG. 1.

FIG. 3 is a section of the memory cell taken along line B-B' of FIG. 1.

FIG. 4 is a top plan view showing the memory cell (for about four) ofthe SRAM of this first embodiment according to the present invention.

FIG. 5 is an equivalent circuit diagram of the memory cell of the SRAMof the first embodiment according to the present invention.

FIG. 6 is a top plan view showing a method for manufacturing the memorycell of the SRAM of the first embodiment according to the presentinvention.

FIGS. 7(a) and 7(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this first embodiment according to thepresent invention.

FIGS. 8(a) and 8(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this first embodiment according to thepresent invention.

FIG. 9 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this first embodiment according to thepresent invention.

FIGS. 10(a) and 10(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this first embodiment according to thepresent invention.

FIGS. 11(a) and (b) are sections showing the method for manufacturingthe memory cell of the SRAM of this first embodiment according to thepresent invention.

FIG. 12 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this first embodiment according to thepresent invention.

FIGS. 13(a) and (b) are sections showing the method for manufacturingthe memory cell of the SRAM of this first embodiment according to thepresent invention.

FIG. 14 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this first embodiment according to thepresent invention.

FIGS. 15(a) and 15(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this first embodiment according to thepresent invention.

FIGS. 16(a) and 16(b) are sections showing the method for manufacturingthe memory cell of the SRAM of the first embodiment according to thepresent invention.

FIG. 17 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this first embodiment according to thepresent invention.

FIGS. 18(a) and 18(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this first embodiment according to thepresent invention.

FIG. 19 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this first embodiment according to thepresent invention.

FIGS. 20(a) and 20(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this first embodiment according to thepresent invention.

FIG. 21 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this first embodiment according to thepresent invention.

FIGS. 22(a) and 22(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this first embodiment according to thepresent invention.

FIG. 23 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this first embodiment according to thepresent invention.

FIGS. 24(a) and 24(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this first embodiment according to thepresent invention.

FIG. 25 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this first embodiment according to thepresent invention.

FIGS. 26(a) and 26(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this first embodiment according to thepresent invention.

FIG. 27 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this first embodiment according to thepresent invention.

FIG. 28 is a section showing the method for manufacturing the memorycell of the SRAM of this first embodiment according to the presentinvention.

FIG. 29 is a section showing the method for manufacturing the memorycell of the SRAM of this first embodiment according to the presentinvention.

FIG. 30 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this first embodiment according to thepresent invention.

FIG. 31 is a section showing the method for manufacturing the memorycell of the SRAM of this first embodiment according to the presentinvention.

FIG. 32 is a section showing the method for manufacturing the memorycell of the SRAM of this first embodiment according to the presentinvention.

FIG. 33 is a top plan view showing a memory cell of an SRAM of a secondembodiment according to the present invention.

FIG. 34 is a section of the memory cell taken along line A-A' of FIG.33.

FIG. 35 is a section of the memory cell taken along line B-B' of FIG.33.

FIG. 36 is an equivalent circuit diagram showing the memory cell of theSRAM of this second embodiment according to the present invention.

FIG. 37 is a top plan view showing a method for manufacturing the memorycell of the SRAM of this second embodiment according to the presentinvention.

FIGS. 38(a) and 38(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this second embodiment according to thepresent invention.

FIG. 39 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this second embodiment according to thepresent invention.

FIGS. 40(a) and 40(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this second embodiment according to thepresent invention.

FIG. 41 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this second embodiment according to thepresent invention.

FIGS. 42(a) and 42(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this second embodiment according to thepresent invention.

FIG. 43 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this second embodiment according to thepresent invention.

FIGS. 44(a) and 44(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this second embodiment according to thepresent invention.

FIG. 45 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this second embodiment according to thepresent invention.

FIGS. 46(a) and 46(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this second embodiment according to thepresent invention.

FIG. 47 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this second embodiment according to thepresent invention.

FIGS. 48(a) and 48(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this second embodiment according to thepresent invention.

FIG. 49 is a top plan view showing a method for manufacturing a memorycell of an SRAM of a third embodiment according to the presentinvention.

FIG. 50 is a section showing the method for manufacturing the memorycell of the SRAM of this third embodiment according to the presentinvention.

FIG. 51 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this third embodiment according to thepresent invention.

FIG. 52 is a section showing the method for manufacturing the memorycell of the SRAM of this third embodiment according to the presentinvention.

FIG. 53 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this third embodiment according to thepresent invention.

FIG. 54 is a section showing the method for manufacturing the memorycell of the SRAM of this third embodiment according to the presentinvention.

FIG. 55 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this third embodiment according to thepresent invention.

FIG. 56 is a section showing the method for manufacturing the memorycell of the SRAM of this third embodiment according to the presentinvention.

FIG. 57 is a section showing the method for manufacturing the memorycell of the SRAM of this third embodiment according to the presentinvention.

FIG. 58 is a section showing the method for manufacturing the memorycell of the SRAM of this third embodiment according to the presentinvention.

FIG. 59 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this third embodiment according to thepresent invention.

FIG. 60 is a section showing the method for manufacturing the memorycell of the SRAM of this third embodiment according to the presentinvention.

FIG. 61 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this third embodiment according to thepresent invention.

FIG. 62 is a section showing the method for manufacturing the memorycell of the SRAM of this third embodiment according to the presentinvention.

FIG. 63 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this third embodiment according to thepresent invention.

FIG. 64 is a section showing the method for manufacturing the memorycell of the SRAM of this third embodiment according to the presentinvention.

FIG. 65 is a top plan view showing a method for manufacturing a memorycell of an SRAM of a fourth embodiment according to the presentinvention.

FIG. 66 is a section showing the method for manufacturing the memorycell of the SRAM of this fourth embodiment according to the presentinvention.

FIG. 67 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this fourth embodiment according to thepresent invention.

FIG. 68 is a section showing the method for manufacturing the memorycell of the SRAM of this fourth embodiment according to the presentinvention.

FIG. 69 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this fourth embodiment according to thepresent invention.

FIG. 70 is a section showing the method for manufacturing the memorycell of the SRAM of this fourth embodiment according to the presentinvention.

FIG. 71 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this fourth embodiment according to thepresent invention.

FIG. 72 is a section showing the method for manufacturing the memorycell of the SRAM of this fourth embodiment according to the presentinvention.

FIG. 73 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this fourth embodiment according to thepresent invention.

FIG. 74 is a section showing the method for manufacturing the memorycell of the SRAM of this fourth embodiment according to the presentinvention.

FIG. 75 is a section showing the method for manufacturing the memorycell of the SRAM of this fourth embodiment according to the presentinvention.

FIG. 76 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this fourth embodiment according to thepresent invention.

FIG. 77 is a section showing the method for manufacturing the memorycell of the SRAM of this fourth embodiment according to the presentinvention.

FIG. 78 is a section showing the method for manufacturing the memorycell of the SRAM of this fourth embodiment according to the presentinvention.

FIG. 79 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this fourth embodiment according to thepresent invention.

FIG. 80 is a section showing the method for manufacturing the memorycell of the SRAM of this fourth embodiment according to the presentinvention.

FIG. 81 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this fourth embodiment according to thepresent invention.

FIG. 82 is a section showing the method for manufacturing the memorycell of the SRAM of this fourth embodiment according to the presentinvention.

FIG. 83 is a top plan view showing the method for manufacturing a memorycell of the SRAM of a fifth embodiment according to the presentinvention.

FIGS. 84(a) and 84(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this fifth embodiment according to thepresent invention.

FIG. 85 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this fifth embodiment according to thepresent invention.

FIGS. 86(a) and (b) are sections showing the method for manufacturingthe memory cell of the SRAM of this fifth embodiment according to thepresent invention.

FIG. 87 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this fifth embodiment according to thepresent invention.

FIGS. 88(a) and 88(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this fifth embodiment according to thepresent invention.

FIG. 89 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this fifth embodiment according to thepresent invention.

FIGS. 90(a) and 90(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this fifth embodiment according to thepresent invention.

FIGS. 91(a) and 91(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this fifth embodiment according to thepresent invention.

FIG. 92 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this fifth embodiment according to thepresent invention.

FIGS. 93(a) and 93(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this fifth embodiment according to thepresent invention.

FIG. 94 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this fifth embodiment according to thepresent invention.

FIGS. 95(a) and 95(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this fifth embodiment according to thepresent invention.

FIG. 96 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this fifth embodiment according to thepresent invention.

FIGS. 97(a) and 97(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this fifth embodiment according to thepresent invention.

FIG. 98 is a top plan view showing the method for manufacturing a memorycell of the SRAM of a sixth embodiment according to the presentinvention.

FIGS. 99(a) and 99(b) are sections showing the method for manufacturingthe memory cell of the SRAM of this sixth embodiment according to thepresent invention.

FIG. 100 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this sixth embodiment according to thepresent invention.

FIGS. 101(a) and 101(b) are sections showing the method formanufacturing the memory cell of the SRAM of this sixth embodimentaccording to the present invention.

FIG. 102 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this sixth embodiment according to thepresent invention.

FIGS. 103(a) and 103(b) are sections showing the method formanufacturing the memory cell of the SRAM of this sixth embodimentaccording to the present invention.

FIG. 104 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this sixth embodiment according to thepresent invention.

FIGS. 105(a) and 105(b) are sections showing the method formanufacturing the memory cell of the SRAM of this sixth embodimentaccording to the present invention.

FIGS. 106(a) and 106(b) are sections showing the method formanufacturing the memory cell of the SRAM of this sixth embodimentaccording to the present invention.

FIGS. 107(a) and 107(b) are sections showing the method formanufacturing the memory cell of the SRAM of this sixth embodimentaccording to the present invention.

FIG. 108 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this sixth embodiment according to thepresent invention.

FIG. 109 is a top plan view showing the method for manufacturing thememory cell of the SRAM of this sixth embodiment according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

While the present invention will be described in connection withspecific and preferred embodiments, it will be understood that it is notintended to limit the invention to those embodiments. To the contrary,it is intended to cover all alterations, modifications and equivalentsas may be included within the spirit and scope of the invention asdefined by the appended claims.

Throughout the present disclosure, where devices are described asincluding or comprising specific components, and methods are describedas comprising or including specific steps, it is contemplated thatdevices of the present invention also consist essentially of, or consistof, the recited components, and methods of the present invention alsoconsist essentially of, or consist of, the recited steps. Accordingly,throughout the present disclosure any described device or process canconsist essentially of, or consist of, the recited components or steps.

The present invention will be described in detail in connection with itsembodiments with reference to the accompanying drawings. Throughout allthe drawings for explaining the embodiments, the portions having thesame functions are designated by the same reference numerals, and theirrepeated description will be omitted.

Embodiment 1

FIG. 5 is an equivalent circuit diagram of a memory cell of an SRAM of afirst embodiment of the present invention. This memory cell is arrangedat the intersection between a pair of complementary data lines (a dataline DL and a data line DL) and a word line WL and is composed of a pairof drive MISFETs Qd₁ and Qd₂, a pair of load MISFETs Qp₁ and Qp₂ and apair of transfer MISFETs Qt₁ and Qt₂. Of these MISFETs, the driveMISFETs Qd₁ and Qd₂ and the transfer MISFETs Qt₁ and Qt₂ are ofp-channel type, and the load MISFETs Qp₁ and Qp₂ are of p-channel type.In short, this memory cell is constructed of a complete CMOS type usingfour n-channel MISFETs and two p-channel MISFETs.

Of the six MISFETs constituting the aforementioned memory cell, thepaired drive MISFETs Qd₁ and Qd₂ and the paired load MISFETs Qp₁ and Qp₂constitute a flip-flop circuit acting as an information storing unit forstoring information of 1 bit. One input/output terminal (a storage node)of this flip-flop circuit is electrically connected with one of thesource and drain regions of the transfer MISFET Qt₁, and the otherinput/output (i.e., a storage node) is electrically connected with oneof the source and drain regions of the transfer MISFET Qt₂.

The data line DL is electrically connected with the other of the sourceand drain regions of the transfer MISFET Qt₁, and the data line DL iselectrically connected with the other of the source and drain regions ofthe transfer MISFET Qt₂. Moreover, one end (each source region of theload MISFETs Qp₁ and QP₂) of the flip-flop circuit is connected with thepower supply voltage (Vcc), and the other (each source region of thedrive MISFETs Qd₁ and Qd₂) is connected with a reference voltage Vss.The power supply voltage (Vcc) is, e.g., 3 V whereas the referencevoltage (Vss) is, e.g., 0 V (GND).

The input/output terminals of the flip-flop circuit are cross-connectedthrough a pair of local wiring lines L₁ and L₂. In the presentembodiment, these paired local wiring lines L₁ and L₂ are arranged indifferent conductive layers, as will be described hereinafter.

A specific construction of the memory cell will be described withreference to FIG. 1 (a top plan view of about one memory cell), FIG. 2(a section taken along line A-A' of FIG. 1), FIG. 3 (a section takenalong line B-B' of FIG. 1) and FIG. 4 (a top plan view of about fourmemory cells). Incidentally, FIGS. 1 and 4 show only connection holesfor connecting the conductive layer constituting the memory cell andupper and lower conductive layers but omit the insulating filmsisolating the individual conductive layers.

The six MISFETs constituting the memory cell are formed in the activeregion which is surrounded by an element isolating groove 2 of asemiconductor substrate 1 made of single crystalline silicon. The driveMISFETs Qd₁ and Qd₂ and the transfer MISFETs Qt₁ and Qt₂ of n-channeltype are formed in the active region of a p-type well 3, and the loadMISFETs Qp₁ and Qp₂ of p-channel type are formed in the active region ofan n-type well 4.

Each of the paired transfer MISFETs Qt₁ and Qt₂ include n-typesemiconductor regions 5 and 5 (the source region and the drain region)formed in the active region of the p-type well 3, a gate oxide film 6formed on the surface of the active region, and a gate electrode 7formed over the gate oxide film 6. The individual gate electrodes 7 ofthe transfer MISFETs Qt₁ and Qt₂ are constructed so as to have apolycide structure, in which an n-type polycrystalline silicon film anda W (tungsten) silicide (WSi₂) film are stacked, for example, and areintegrated with the word line WL. This word line WL is extended in afirst direction (in the lateral direction of FIGS. 1 and 4), and thepaired transfer MISFETs Qt₁ and Qt₂ are arranged adjacent to each otherin the first direction. The paired transfer MISFETs Qt₁ and Qt₂ are soarranged that their gate length direction is a second direction (thevertical direction of FIGS. 1 and 4) perpendicular to the firstdirection.

Channel forming regions of the transfer MISFETs Qt₁ and Qt₂ are formed,in the active region of the p-type well 3, under the gate electrodes 7thereof and between n-type semiconductor regions 5 and 5.

Each of the paired drive MISFETs Qd₁ and Qd₂ is composed of the n-typesemiconductor regions 5 and 5 (the source region and the drain region)formed in the active region of the p-type well 3, the gate oxide film 6formed on the surface of the active region, and a gate electrode 8formed over the gate oxide film 6. The n-type semiconductor region 5(the drain region) of the drive MISFET Qd₁ is formed in the activeregion shared with the n-type semiconductor region (one of the sourceregion and the drain region) of the transfer MISFET Qt₁, and the n-typesemiconductor region 5 (the drain region) of the n-type semiconductorregion 5 of the drive MISFET Qd₂ is formed in the active region sharedwith the n-type semiconductor region 5 (one of the source region and thedrain region) of the transfer MISFET Qt₂. The individual gate electrodes8 of the drive MISFETs Qd₁ and Qd₂ are, illustratively, made to have apolycide structure in which an n-type polycrystalline silicon film and asilicide film are stacked, for example.

Channel forming regions of the driver MISFETs Qd₁ and Qd₂ are formed, inthe active region of the p-type well 3, under the gate electrodes 8thereof and between the source region and the drain region thereof.

Each of the paired load MISFETs Qp₁ and Qp₂ is composed of p-typesemiconductor regions 9 and 9 (the source region and the drain region)formed in the active region of the n-type well region 4, the gate oxidefilm 6 formed on the surface of the active region, and the gateelectrode 8 formed over the gate oxide film 6. The gate electrode 8 ofthe load MISFET Qp₁ is integrated with the gate electrode 8 of the driveMISFET Qd₁, and the gate electrode 8 of the load MISFET QP₂ isintegrated with the gate electrode 8 of the drive MISFET Qd₂.

Channel forming regions of the load MISFETs Qp₁ and Qp₂ are formed, inthe active region of the n-type well 4, under the gate electrodes 8thereof and between the source region and the drain region thereof.

The drive MISFET Qd₁ is arranged in the second direction between theload MISFET Qp₁ and the transfer MISFET Qt₁, and the drive MISFET Qd₂ isarranged in the second direction between the load MISFET Qp₁ and thetransfer MISFET Qt₂. The paired drive MISFETs Qd₁ and Qd₂ and the pairedload MISFETs Qp₁ and Qp₂ are so individually arranged that their gatelength direction is the first direction.

On the surfaces of the individual n-type semiconductor regions 5 and 5(the source regions and the drain regions) of the drive MISFETs Qd₁ andQd₂ and the transfer MISFETs Qt₁ and Qt₂, there are formed Ti (titanium)silicide (TiSi₂) layers for reducing the sheet resistances of the n-typesemiconductor regions 5 and 5. Likewise, on the surfaces of theindividual p-type semiconductor regions 9 and 9 (the source regions andthe drain regions) of the load MISFETs Qp₁ and Qp₂, there are formed theTi-silicide layers for reducing the sheet resistances of the p-typesemiconductor regions 9 and 9.

Side wall spacers 11 of a silicon oxide film are formed on theindividual side walls of the gate electrode 7 (the word line WL) of thetransfer MISFETs Qt₁ and Qt₂ and the gate electrodes 8 of the driveMISFETs Qd₁ and Qd₂ (the load MISFETs Qp₁ and Qp₂). A silicon oxide film(a cap insulating film) 12 is formed over the gate electrode 7 (the wordline WL) and the gate electrode 8.

Over the aforementioned six MISFETs, there is formed a silicon nitridefilm 13, over which is formed one (i.e., the local wiring line L₁) ofthe paired local wiring lines L₁ and L₂. One end portion of this localwiring line L₁ is electrically connected through a connection hole 14,which is opened in the silicon nitride film 13 and the silicon oxidefilm 12, with the gate electrode 8 which is shared by the load MISFETQp₂ and the drive MISFET Qd₂. Another end portion of the local wiringline L₁ is electrically connected through a connection hole 15, which isopened in the silicon nitride film 13, with the n-type semiconductorregion 5 (the drain region) of the drive MISFET Qd₁. Still another endportion of the local wiring line L₁ is electrically connected through aconnection hole 16, which is opened in the silicon nitride film 13, withthe p-type semiconductor region 9 (the drain region) of the load MISFETQp₁. In short, the local wiring line L₁ connects the gate electrode 8 ofthe drive MISFET Qd₂ (the load MISFET Qp₂), the n-type semiconductorregion 5 (the drain region) of the drive MISFET Qd₁ and the p-typesemiconductor region 9 (the drain region) of the load MISFET Qp₁ withone another. The local wiring line L₁ is formed of a TiN (titaniumnitride) film, for example. The local wiring line L₁ can be made ofmaterials other than TiN, a refractory metal such as W or a refractorymetal silicide such as a W-silicide.

The local wiring line L₁ is formed over the channel forming regions ofthe driver MISFETs Qd₁ and Qd₂, of the load MISFETs Qp₁ and Qp₂, and ofthe transfer MISFETs Qt₁ and Qt₂.

Over the local wiring line L₁, there is formed the other (the localwiring line L₂) of the paired local wiring lines L₁ and L₂ through aninterlayer insulating film 17 of a first layer which is formed of asilicon oxide insulating film of PSG (Phospho Silicate Glass). One endportion of the local wiring line L₂ is electrically connected through aconnection hole 18, which is opened in the silicon nitride film 13 andthe silicon oxide film 12, with the gate electrode 8 which is shared bythe load MISFET Qp₁ and the drive MISFET Qd₁. Another end portion of thelocal wiring line L₂ is electrically connected through a connection hole19, which is opened in the interlayer insulating film 17 and the siliconnitride film 13, with the n-type semiconductor region 5 (the drainregion) of the drive MISFET Qd₂. Still another end portion of the localwiring line L₂ is electrically connected through a connection hole 20,which is opened in the interlayer insulating film 17 and the siliconnitride film 13, with the p-type semiconductor region 9 (the drainregion) of the load MISFET Qp₂. In short, the local wiring line L₂connects the gate electrode 8 of the drive MISFET Qd₁ (the load MISFETQp₁), the n-type semiconductor region 5 (the drain region) of the driveMISFET Qd₂ and the p-type semiconductor region 9 (the drain region) ofthe load MISFET Qp₂ electrically with one another. The local wiring lineL₂ is composed of an Al (aluminum) film which is overlaid and underlaidwith barrier metal layers of TiN, for example. In the connection holes18, 19 and 20 thus far described, moreover, there is buried plugs 29which are composed of a W-film for ensuring the reliability ofelectrical connection between the local wiring line L₂ and the gateelectrode 8, and electrical connection between the n-type semiconductorregion and the p-type semiconductor region 9.

The local wiring line L₂ is formed over the channel forming regions ofthe driver MISFETs Qd₁ and Qd₂, of the local MISFETs Qp₁ and Qp₂, and ofthe transfer MISFETs Qt₁ and Qt₂.

Over the local wiring line L₂ there are formed, through an interlayerinsulating film 21 of a second layer made of silicon oxide, a powersupply voltage line 22 and a reference voltage line 23. The power supplyvoltage line 22 is electrically connected through a connection hole 24,which is opened in the interlayer insulating films 21 and 17 and thesilicon nitride film 13, with the individual p-type semiconductorregions 9 (the source regions) of the load MISFETs Qp₁ and Qp₂ to supplythese p-type semiconductor regions 9 with the power supply voltage(Vcc). The reference voltage line 23 is electrically connected through aconnection hole 25, which is opened in the interlayer insulating films21 and 17 and the silicon nitride film 13, with the individual n-typesemiconductor regions (the source regions) of the drive MISFETs Qd₁ andQd₂ to supply the n-type semiconductor regions with the referencevoltage (Vss). The power supply voltage line 22 and the referencevoltage line 23 are composed of an Al film which is overlaid andunderlaid with barrier metal layers, for example. In the connectionholes 24 and 25, there are buried plugs 37 which are composed of aW-film, for example, for ensuring the reliability of electricalconnection between the power supply voltage line 22 and the p-typesemiconductor region 9, and electrical connection between the referencevoltage line 23 and the n-type semiconductor region 5.

Over the power supply voltage line 22 and the reference voltage line 23,there are formed, through an interlayer insulating film 26 of a thirdlayer made of silicon oxide, the paired complementary data lines (thedata line DL and the data line DL). One (the data line DL) of thesecomplementary data lines is electrically connected through a connectionhole 27, which is opened in the interlayer insulating films 26, 21 and17 and the silicon nitride film 13, with the n-type semiconductor region5 (the other of the source region and the drain region) of the transferMISFET Qt₁. The other (the data line DL) of the complementary data linesis electrically connected through the connection hole 27, which isopened in the interlayer insulating films 26, 21 and 17 and the siliconnitride film 13, with the n-type semiconductor region 5 (the other ofthe source region and the drain region) of the transfer MISFET Qt₂. Thedata line DL and the data line DL are composed of Al films which areoverlaid and underlaid with barrier metal layers of TiN. In theconnection holes 27 and 27, although not shown, there are buried plugswhich are composed of W-films for ensuring the reliability of electricalconnection between the data lines (DL and DL) and the n-typesemiconductor region 5.

Thus, in the SRAM of the present embodiment, the paired local wiringlines L₁ and L₂ cross-connecting the input/output terminals of theflip-flop circuit of the memory cell are formed in the differentconductive layers. Thanks to this construction, the space, which isrequired for arranging the two local wiring lines transversely when thepaired local wiring lines are formed in the same conductive layer, isnot required, so that the local wiring lines L₁ and L₂ can be arrangedpartially in an overlapping manner, thereby reducing the area occupiedby the memory cell.

A method for manufacturing the memory cell of the SRAM of the presentembodiment will be described with reference to FIGS. 6 to 32. Of theseshowing the memory cell manufacturing method, sections (a) are takenalong line A-A' of the top plan views, and sections (b) are taken alongline B-B' of the top plan views. These individual top plan views showonly the conductive layers and the connection holes but do not show theinsulating films.

First of all, a groove 30 is formed in the periphery (element isolatingregion) of an active region AR of the major face of the semiconductorsubstrate 1 made of p-type single crystal silicon, as shown in FIGS. 6and 7(a) and (b). This groove 30 is formed by depositing a silicon oxidefilm 31 and a silicon nitride film 32 consecutively over thesemiconductor substrate 1 and then by dry-etching the silicon nitride32, the silicon oxide film 31 and the semiconductor substrate 1consecutively by using a photoresist as the mask.

Next, a silicon oxide film 36 is buried in the groove 30 to form theelement isolating groove 2, as shown in FIGS. 8(a) and 8(b). The elementisolating groove 2 is formed by depositing the silicon oxide film 36thickly over the semiconductor substrate 1, including the inside of thegroove 30, by a CVD (Chemical Vapor Deposition) method and then byetching back (chemico-mechanical polishing (CMP)) the silicon oxide film36 by using the silicon nitride film 32 as an etching stopper.

Next, the silicon nitride film 32 and the silicon oxide film 31, left onthe surface of the active region AR, are etched away. After this, asshown in FIGS. 9 and 10(a) and 10(b), the semiconductor substrate 1 ofthe active region AR where the drive MISFETs Qd₁ and Qd₂ and thetransfer MISFETs Qt₁ and Qt₂ are formed is doped with ions of p-typeimpurity (boron) to form the p-type well 3, and the semiconductorsubstrate 1 of the active region AR where the load MISFETs Qp₁ and Qp₂are formed is doped with ions of an n-type impurity (phosphorous orarsenic) to form the n-type well 4. After this, the individual surfacesof the p-type well 3 and the n-type well 4 are thermally oxidized toform the gate oxide film 6.

Next, an n-type polycrystalline silicon film 33, a W-silicide film 34and the silicon oxide film 12 are consecutively deposited over thesemiconductor substrate 1 by a CVD method, as shown in FIG. 11(a) and(b). After this, the silicon oxide film 12, the W-silicide film 34 andthe n-type polycrystalline silicon film 33 are patterned by using aphotoresist as the mask, as shown in FIGS. 12 and 13(a) and 13(b), toform the gate electrode 7 (the word line WL) of the transfer MISFETs Qt₁and Qt₂ and the gate electrodes 8 and 8 of the drive MISFETs Qd₁ and Qd₂(the load MISFITs Qp₁ and Qp₂).

Next, as shown in FIGS. 14 and 15(a) and 15(b), the p-type well 3 isdoped with ions of n-type impurity (phosphorous or arsenic) to form then-type semiconductor regions 5 and 5 (the source region and the drainregion) of the transfer MISFETs Qt₁ and Qt₂, and the drive MISFETs Qd₁and Qd₂, and the n-type well 4 is doped with the ions of p-type impurity(boron) to form the p-type semiconductor regions 9 and 9 (the sourceregion and the drain region) of the load MISFETs Qp₁ and Qp₂. Afterthis, the silicon oxide film, deposited over the semiconductor substrate1 by a CVD method, is anisotropically etched to form the side wallspacers 11 on the individual side walls of the gate electrode 7 (theword line WL) of the transfer MISFETs Qt₁ and Qt₂ and the gateelectrodes 8 and 8 of the drive MISFETs Qd₁ and Qd₂.

Next, there are etched the gate oxide film covering the surfaces of theindividual n-type semiconductor regions 5 and 5 (the source region andthe drain region) of the drive MISFETs Qd₁ and Qd₂ and the transferMISFETs Qt₁ and Qt₂, and the gate oxide film 6 covering the surfaces ofthe p-type semiconductor regions 9 and 9 (the source region and thedrain region) of the load MISFETs Qp₁ and Qp₂. After this, as shown inFIG. 16, a Ti-film 35 is deposited over the semiconductor substrate 1 bysputtering.

Next the semiconductor substrate 1 is annealed (thermally treated) tocause a reaction between the Ti-film 35 and the semiconductor substrate1 (the n-type semiconductor region 5 and the p-type semiconductor region9). After this, the unreacted Ti-film 35 is etched to form theTi-silicide layer 10 on the surfaces of the p-type semiconductor region5 and the p-type semiconductor region 9, as shown in FIGS. 17 and 18(a)and 18(b). After this, the semiconductor substrate 1 is annealed, ifnecessary, to reduce the resistance of the Ti-silicide layer 10. Insteadof forming the Ti-silicide layer 10, a Co (cobalt) film may be formedover the semiconductor substrate 1 by sputtering to cause a reactionbetween the semiconductor substrate 1 (the n-type semiconductor region 5and the p-type semiconductor region 9) and the Co film, thereby to forma Co-silicide layer.

Next, the silicon nitride film 13, as thin as about 30 nm, is depositedover the semiconductor substrate 1, as shown in FIGS. 19 and 20(a) and(b). After this, the connection hole 14 is opened in the silicon nitridefilm 13 and the silicon oxide film 12 over the gate electrodes 8 of thedrive MISFET Qd₂ (or the load MISFET Qp₂) by a dry-etching method usinga photoresist as the mask. Simultaneously with this, the silicon nitridefilm 13 over the n-type semiconductor region 5 (the drain region) of thedrive MISFET Qd₁ is etched off to form the connection hole 15, and thesilicon nitride film 13 over the p-type semiconductor region 9 (thedrain region) of the load MISFET Qp₁ is etched to form the connectionhole 16. Next, the local wiring line L₁ is formed over the siliconnitride film 13, as shown in FIGS. 21 and 22(a) and (b). The localwiring line L₁ is formed by patterning the TiN film, having a thicknessof about 100 nm and deposited over the semiconductor substrate 1 by asputtering method or a CVD method, by a dry-etching method using aphotoresist as the mask. This local wiring line L₁ is connected throughthe connection hole 14 with the common gate electrode 8 of the loadMISFET Qp₂ and the drive MISFET Qd₂, through the connection hole 15 withthe n-type semiconductor region 5 (the drain region) of the drive MISFETQd₁, and through the connection hole 16 with the p-type semiconductorregion 9 (the drain region) of the load MISFET Qp₁.

Next, the interlayer insulating film 17 of PSG is deposited over thelocal wiring line L₁ by the CVD method, as shown in FIGS. 23 and 24(a)and (b). After this, the interlayer insulating film 17, the siliconnitride film 13 and the silicon oxide film 12 lying over the gateelectrode 8 of the drive MISFET Qd₁ (the load MISFET Qp₁) are opened toform the connection hole 18 by a dry-etching technique using aphotoresist as the mask. Simultaneously with this, the interlayerinsulating film 17 and the silicon nitride film 13 over the n-typesemiconductor region 5 (the drain region) of the drive MISFET Qd₂ areetched to form the connection hole 19, and the interlayer insulatingfilm 17 and the silicon nitride film 13 over the p-type semiconductorregion 9 (the drain region) of the load MISFET Qp₂ are etched to formthe connection hole 20.

Next, W-films are buried in the connection holes 18, 19 and 20 to formthe plugs 29, as shown in FIGS. 25 and 26(a) and (b). After this, thelocal wiring line L₂ is formed over the interlayer insulating film 17.The burying operation of the W-film is carried out by etching back theW-film which is deposited over the interlayer insulating film 17 by asputtering method. The local wiring line L₂ is formed by depositing theTiN film, the Al film and the TiN film consecutively over the interlayerinsulating film 17 by a sputtering method and then by patterning thosefilms by a dry-etching method using a photoresist as the mask. The localwiring line L₂ is connected through the connection hole 18 with thecommon gate 8 of the load MISFET Qp₁ and the drive MISFET Qd₁, throughthe connection hole 19 with the n-type semiconductor region 5 (the drainregion) of the drive MISFET Qd₂, and through the connection hole 20 withthe p-type semiconductor region 9 (the drain region) of the load MISFETQp₂.

Next, the interlayer insulating film 21 of silicon oxide is depositedover the local wiring line L₂ by a CVD method, as shown in FIGS. 27, 28and 29. After this, the interlayer insulating films 21 and 17 and thesilicon nitride film 13 over the individual p-type semiconductor regions9 and 9 (the source regions) of the load MISFETs Qp₁ and Qp₂ are openedto form the connection holes 24 and 24 by the dry-etching method, usinga photoresist as the mask. Simultaneously with this, the interlayerinsulating films 21 and 17 and the silicon nitride film 13 over theindividual n-type semiconductor regions 5 and 5 (the source regions) ofthe drive MISFETs Qd₁ and Qd₂ are opened to form the connection holes 25and 25.

Next, W-films are buried in the connection holes 24 and 25 to form theplug 37. After this, as shown in FIGS. 30, 31 and 32, the power supplyvoltage line 22 and the reference voltage line 23 are formed over theinterlayer insulating film 21. These power supply and reference voltagelines 22 and 23 are formed by depositing a TiN film, an Al film and aTiN film consecutively over the interlayer insulating film 21 by asputtering method, and then by patterning those films by a dry-etchingmethod using a photoresist as the mask. The power supply voltage line 22is connected through the connection holes 24 and 24 with the individualp-type semiconductor regions 9 and 9 (the source regions) of the loadMISFETS Qp₁ and Qp₂, and the reference voltage line 23 is connectedthrough the connection holes 25 and 25 with the individual n-typesemiconductor regions 5 and 5 (the source regions) of the drive MISFETSQd₁ and Qd₂.

After this, the interlayer insulating film 26 of silicon oxide isdeposited over the power supply voltage line 22 and the referencevoltage line 23 by a CVD method. After this, the interlayer insulatingfilms 26, 21 and 17 and the silicon nitride film 13 over the individualn-type semiconductor regions 5 and 5 (the drain regions) of the transferMISFETs Qt₁ and Qt₂ are opened to form the connection holes 27 and 27 bya dry-etching method using a photoresist as the mask. Subsequently,W-films are buried in the connection holes 27 and 27 to form plugs, andthe data lines DL and DL are then formed over the interlayer insulatingfilm 26. These data lines DL and DL are formed by depositing a TiN film,an Al film and a TiN film consecutively over the interlayer insulatingfilm 26 by a sputtering method, and then by patterning those films by adry-etching method using a photoresist as the mask. The data line DL isconnected through one of the connection holes 27 and 27 with the n-typesemiconductor region 5 (the drain region) of the transfer MISFET Qt₁,and the data line DL is connected through the other of the connectionholes 27 and 27 with the n-type semiconductor region 5 (the drainregion) of the transfer MISFET Qt₂. The memory cell, as shown in FIGS. 1to 4, is thus completed by the steps described.

Embodiment 2

FIG. 33 is a top plan view showing a memory cell of an SRAM of thepresent embodiment; FIG. 34 is a section taken along line A-A' of FIG.33; FIG. 35 is a section taken along line B-B' of FIG. 33; and FIG. 36is an equivalent circuit diagram showing the memory cell of the SRAM ofthe present embodiment.

In the SRAM of the present embodiment, as shown, the paired local wiringlines L₁ and L₂ cross-connecting the input/output terminals of theflip-flop circuit of the memory cell are formed in different conductivelayers, as in the SRAM of the foregoing embodiment 1. In the SRAM of thepresent embodiment, moreover, the upper local wiring line L₂ overlapswith the lower local wiring line L₁ over a wide area, and a capacitorelement C is composed of the local wiring lines L₁ and L₂ and a thininsulating film (a silicon nitride film 42) interposed between thewiring lines. Specifically, the upper local wiring line L₂ is oneelectrode of the capacitor element C, the lower local wiring line L₁ isthe other electrode, and the insulating film (the silicon nitride film42) is its dielectric film.

A method for manufacturing the memory cell of the SRAM of the presentembodiment will be described with reference to FIGS. 37, 38(a) and (b),39, 40(a) and (b), 41, 42(a) and (b), 43, 44(a) and (b) 45, 46(a) and(b), 47 and 48(a) and (b). Of the individual Figures showing the memorycell manufacturing method, sections (a) are taken along line A-A' of thetop plan views, and sections (b) are taken along line B-B' of the topplan views. Moreover, the individual top plan views show only theconductive layers and the connection holes but do not show theinsulating films.

First of all, in accordance with the manufacturing method of theforegoing embodiment 1, as shown in FIGS. 6 et seq., up to and includingFIGS. 18(a) and (b), an element isolating groove 2, a p-type well 3, ann-type well 4 and a gate oxide film 6 are formed over a major face ofthe semiconductor substrate 1. After this, drive MISFETs Qd₁ and Qd₂ andtransfer MISFETs Qt₁ and Qt₂ are formed in a p-type well 3, and loadMISFETs Qp₁ and Qp₂ are formed in an n-type well 4. Moreover, aTi-silicide layer 10 is formed so as to reduce the sheet resistance overthe surfaces of n-type semiconductor regions 5 and 5 (the source regionand the drain region) of the transfer MISFETs Qt₁ and Qt₂ and the driveMISFETs Qd₁ and Qd₂ and over the surfaces of p-type semiconductorregions 9 and 9 (the source region and the drain region) of the loadMISFETs Qp₁ and Qp₂.

Next, as shown in FIGS. 37 and 38(a) and (b), a silicon nitride film 13,as thick as about 50 nm, is deposited over the semiconductorsubstrate 1. After this, the silicon nitride film 13 and a silicon oxidefilm 12 over a gate electrode 8 of the drive MISFET Qd₂ (or the loadMISFET Qp₂) are opened to form a connection hole 14 by a dry-etchingmethod using a photoresist as the mask. Simultaneously with this, thesilicon nitride film 13 over the n-type semiconductor region 5 (thedrain region) of the drive MISFET Qd₁ is etched to form a connectionhole 40, and the silicon nitride film 13 over the p-type semiconductorregion 9 (the drain region) of the load MISFET Qp₁ is etched to form aconnection hole 41.

Next, as shown in FIGS. 39 and 40(a) and (b), a local wiring line L₁ isformed over the silicon nitride film 13. This local wiring line L₁ isformed by patterning a TiN film, having a thickness of about 100 nm anddeposited over the silicon nitride film 13 by a sputtering method or aCVD method, by a dry-etching method using a photoresist as the mask. Thelocal wiring line L₁ is given an area wide enough to cover the sixMISFETs constituting the memory cell. Specifically, the local wiringline L₁ is so arranged as to cover the gate electrode 8 of the driveMISFET Qd₁ (the load MISFET Qp₁), the gate electrode 8 of the driveMISFET Qd₂ (the load MISFET Qp₂), the gate electrode 7 (the word lineW1) of the transfer MISFETs Qt₁ and Qt₂, the common n-type semiconductorregion (one of the source region and the drain region) of the transferMISFETs Qt₁ and Qt₂ and the drive MISFETs Qd₁ and Qd₂, and the p-typesemiconductor region 9 (the drain region) of the load MISFETs Qp₁ andQp₂.

The local wiring line L₁ is connected through the connection hole 14with the gate electrode 8 of the drive MISFET Qd₂ (the load MISFET Qp₂),through the connection hole 40 with the n-type semiconductor region 5(the drain region) of the drive MISFET Qd₁, and through the connectionhole 41 with the p-type semiconductor region 9 (the drain region) of theload MISFET Qp₁.

Next, as shown in FIGS. 41 and 42(a) and (b), a silicon nitride film 42having a thickness of about 30 nm is deposited over the local wiringline L₁. After this, the silicon nitride films 17 and 13 and the siliconoxide film 12 over the gate electrode 8 of the drive MISFET Qd₁ (theload MISFET Qp₁) are opened to form a connection hole 18 by adry-etching method using a photoresist as the mask. Simultaneously withthis, the silicon nitride films 17 and 13 over the n-type semiconductorregion 5 (the drain region) of the drive MISFET Qd2 are etched to formthe connection hole 19, and the silicon nitride films 17 and 13 over thep-type semiconductor region 9 (the drain region) of the load MISFET Qp₂are etched to form a connection hole 20.

Next, as shown in FIGS. 43 and 44(a) and (b), a local wiring line L₂ isformed over the silicon nitride film 42. This local wiring line L₂ isformed by patterning the TiN film, which is so deposited as to have athickness of about 100 nm by a sputtering method or a CVD method, by adry-etching method using a photoresist as the mask. The local wiringline L₂ can be made of not only TiN but also a refractory metal such asW or a refractory metal silicide such as W-silicide. The local wiringline L₂ is connected through the connection hole 18 with the gateelectrode 8 of the drive MISFET Qd₁ (the load MISFET Qp₁), through theconnection hole 19 with the n-type semiconductor region 5 (the drainregion) of the drive MISFET Qd₂, and through the connection hole 20 withthe p-type semiconductor region 9 (the drain region) of the load MISFETQp₁.

The local wiring line L₂ is so formed over the lower local wiring lineL₁ as to have an area wide enough to cover the six MISFETs constitutingthe memory cell and is substantially completely superposed on the localwiring line L₁ in the region excepting the open regions of theconnection holes 18, 19 and 20 and their registration allowance region.As a result, the capacitor element C can be composed of both the localwiring lines L₁ and L₂ and the silicon nitride film 42 (the dielectricfilm) interposed therebetween and made thinner than the local wiringlines L₁ and L₂, and can be given a large capacitance, so that theamount of stored charge of the storage node can be increased to improvethe alpha particle soft error resistance of the memory cell. If,moreover, the thin insulating film, interposed between the local wiringlines L₁ and L₂, is made of a highly dielectric material such astantalum pentoxide (Ta₂ O₅), the amount of stored charge of the storagenode can be further increased.

Next, as shown in FIGS. 45 and 46(a) and (b), an interlayer insulatingfilm 21 made of silicon oxide is deposited over the local wiring line L₂by a CVD method. After this, the interlayer insulating film 21 and thesilicon nitride films 17 and 13 over the individual p-type semiconductorregions 9 and 9 (the source regions) of the load MISFETs Qp₁ and Qp₂ areopened to form connection holes 24 and 24 by a dry-etching method usinga photoresist as the mask. Simultaneously with this, the interlayerinsulating film 21 and the silicon nitride films 17 and 13 over theindividual n-type semiconductor regions 5 and 5 (the source regions) ofthe drive MISFETs Qd₁ and Qd₂ are opened to form connection holes 25 and25.

Next, as shown in FIGS. 47 and 48(a) and (b), W-films are buried in theconnection holes 24 and 25 to form plugs 29, and power supply voltageline 22 and reference voltage line 23 are then formed over theinterlayer insulating film 21. These power supply and reference voltagelines 22 and 23 are formed by depositing a TiN film, an Al film and aTiN film consecutively over the interlayer insulating film 21 by asputtering method, and then by patterning those films.

After this, an interlayer insulating film 26 of silicon oxide isdeposited over the power supply voltage line 22 and the referencevoltage line 23 by a CVD method. After this, the interlayer insulatingfilms 26 and 21 and the silicon nitride films 17 and 13 over theindividual n-type semiconductor regions 5 and 5 (the drain regions) ofthe transfer MISFETs Qt₂ and Qt₂ are opened to form connection holes 27and 27 by a dry-etching method using a photoresist as the mask.Subsequently, W-films are buried in the connection holes 27 and 27 toform plugs, and the data lines DL and DL are then formed over theinterlayer insulating film 26. These data lines DL and DL are formed bydepositing a TiN film, an Al film and a TiN film consecutively over theinterlayer insulating film 26 by a sputtering method and then bypatterning those films. The memory cell, as shown in FIGS. 33 to 35, isthus completed by the steps described.

Embodiment 3

In the SRAM of the present embodiment, the paired local wiring lines L₁and L₂ cross-connecting the input/output terminals of the flip-flopcircuit of the memory cell are formed in the same conductive layer. Themethod for manufacturing the memory cell of this SRAM will be describedwith reference to FIGS. 49 to 64. Of the individual Figures showing thememory cell manufacturing method, sections are taken along line C-C' ofthe top plan views. Moreover, the individual top plan views show onlythe conductive layers and the connection holes but do not show theinsulating films.

First of all, as shown in FIGS. 49 and 50, a p-type well 3 and a n-typewell 4 are formed over the principal face of a semiconductor substrate1, and an element isolating field oxide film 28 and a gate oxide film 6of a MISFET are then formed over those surfaces. After this, driveMISFETs Qd₁ and Qd₂ and transfer MISFETs Qt₁ and Qt₂ are formed in thep-type well 3, and load MISFETs Qp₁ and Qp₂ are formed in the n-typewell 4. A gate electrode 7 (the word line WL) of the transfer MISFETsQt₁ and Qt₂ and gate electrodes 8 and 8 of the drive MISFETs Qd₁ and Qd₂(the load MISFETs Qp₁ and Qp₂) are formed of a polycrystalline siliconfilm having a thickness of about 300 nm. Side wall spacers on theindividual side walls of the gate electrode 7 (the word line WL) and thegate electrode 8 are formed by etching a silicon oxide film.

Next, as shown in FIGS. 51 and 52, in order to reduce the sheetresistance, a Ti-silicide layer 10 is formed on the individual surfacesof the gate electrode 7 (the word line WL) of the transfer MISFETs Qt₁and Qt₂, the gate electrodes 8 and 8 of the drive MISFETs Qd₁ and Qd₂(the load MISFETs Qp₁ and Qp₂), individual n-type semiconductor regions5 and 5 (the source region and the drain region) of the transfer MISFETsQt₁ and Qt₂ and the drive MISFETs Qd₁ and Qt₂, and individual p-typesemiconductor regions 9 and 9 of the load MISFETs Qp₁ and Qp₂.

In order to form the Ti-silicide layer 10, a silicon oxide film 12covering the individual surfaces of the gate electrode 7 (the word lineWL) and the gate electrode 8, a gate oxide film 6 covering the surfacesof the individual n-type semiconductor regions 5 and 5 (the sourceregion and the drain region) of the drive MISFETs Qd₁ and Qd₂ and thetransfer MISFETs Qt₁ and Qt₂, and a gate oxide film 6 covering thesurfaces of the individual p-type semiconductor regions 9 and 9 (thesource region and the drain region) of the load MISFETs Qp₁ and Qp₂ areetched. After this, a Ti-film is deposited over the semiconductorsubstrate 1 by sputtering. Next, the semiconductor substrate 1 isannealed to cause reactions individually between the Ti-film and thesemiconductor substrate 1 (the n-type semiconductor region 5 and thep-type semiconductor region 9) and between the Ti-film and thepolycrystalline silicon film (the gate electrodes 7 and 8), and theunreacted Ti-film is then etched away.

Next, as shown in FIGS. 53 and 54, a silicon nitride film 13, as thin asabout 30 nm, is deposited over the semiconductor substrate 1 by a CVDmethod. After this, the silicon nitride film 13 is dry-etched by using aphotoresist as the mask to form a connection hole 43, which reaches then-type semiconductor region 5 (the drain region) of the drive MISFET Qd₁and the gate electrode 8 of the drive MISFET Qd₂ (the load MISFET Qp₂),and a connection hole 44 which reaches the p-type semiconductor region 9(the drain region) of the load MISFET QP2 and the gate electrode 8 ofthe drive MISFET Qd1 (the load MISFET Qp₁). Simultaneously with this, aconnection hole 45 is formed over the n-type semiconductor region 5 (thedrain region) of the drive MISFET Qd₂, and a connection hole 46 isformed over the p-type semiconductor region 9 (the drain region) of theload MISFET Qp₁. At this time, the surface of a field oxide film 28 iscovered with the silicon nitride film 13, so that it is not removed bythe dry-etching treatment.

Next, as shown in FIGS. 55 and 56, the paired local wiring lines L₁ andL₂, composed of a TiN film, are formed over the silicon nitride film 13.For forming these local wiring lines L₁ and L₂, a TiN film having athickness of about 50 to 100 nm is deposited over the silicon nitridefilm 13 by a sputtering method or a CVD method. Next, a silicon nitridefilm 47 having a thickness of about 100 nm is deposited over the TiNfilm by a CVD method. After this, the silicon nitride film 47 and theTiN film are patterned by a dry-etching method using a photoresist asthe mask. The local wiring lines L₁ and L₂ can be made of not only TiNbut also a refractory metal such as W or a refractory metal silicidesuch as a W-silicide.

The local wiring line L₁ is so arranged as to overlap with the gateelectrode 8 of the drive MISFET Qd₁ (the load MISFET Qp₁) and the gateelectrode 7 (the word line WL) of the transfer MISFETs Qt₁ and Qt₂, andthe local wiring line L₂ is so arranged as to overlap with the gateelectrode 8 of the drive MISFIT Qd₂ (the load MISFET Qp₂) and the gateelectrode 7 (the word line WL) of the transfer MISFETs Qt₁ and Qt₂.Thanks to this construction, a capacitor element C' is composed of thelocal wiring line L₁, the gate electrode 8 and the thin silicon nitridefilm 13 interposed therebeween, and a capacitor element C' is formed ofthe local wiring line L₂, the gate electrode 8 and the silicon nitridefilm 13 interposed therebetween, so that the charge storage capacity ofthe storage node can be increased to improve the alpha particle softerror resistance of the memory cell. These capacitor elements C' acteffectively similarly to those of the capacitor element C of theforegoing embodiment 2 (of FIG. 36).

The local wiring line L₁ is connected through the connection hole 43with the n-type semiconductor region 5 (the drain region) of the driveMISFET Qd₁ and the gate electrode 8 of the drive MISFET Qd₂ (the loadMISFET Qp₂), and through the connection hole 46 with the p-typesemiconductor region 9 (the drain region) of the load MISFET Qp₁. Inother words, the gate electrode 8 of the drive MISFET Qd₂ (the loadMISFET Qp₂), the n-type semiconductor region 5 (the drain region) of thedrive MISFET Qd₁, and the p-type semiconductor region 9 (the drainregion) of the load MISFET Qp₁ are connected with one another throughthe local wiring line L₁.

The local wiring line L₂ is connected through the connection hole 44with the p-type semiconductor region 9 (the drain region) of the loadMISFET Qp₂ and the gate electrode 8 of the drive MISFET Qd₁ (the loadMISFET Qp₁), and through the connection hole 45 with the n-typesemiconductor region 5 (the drain region) of the drive MISFET Qd₂. Inother words, the gate electrode 8 of the drive MISFET Qd₁ (the loadMISFET Qp₁), the n-type semiconductor region 5 (the drain region) of thedrive MISFET Qd₂, and the p-type semiconductor region 9 (the drainregion) of the load MISFET Qp₂ are connected with one another throughthe local wiring line L₂.

Next, as shown in FIG. 57, a silicon nitride film 53 having a thicknessof about 200 nm is deposited over the silicon nitride film 47 by a CVDmethod. After this, as shown in FIG. 58, this silicon nitride film 53 isanisotropically etched by a RIE (Reactive Ion Etching) method to formside wall spacers 48 on the individual side walls of the gate electrode7 (the word line WL), the gate electrode 8 and the local wiring lines L₁and L₂.

Next, as shown in FIGS. 59 and 60, an interlayer insulating film 49 of asilicon oxide, such as PSG, of an etching rate different from that ofthe silicon nitride films 47 and 53 (the side wall spacer 48) isdeposited by a CVD method over the silicon nitride film 47 and the sidewall spacers 48. The etching rate of the material of insulating film 49is greater than that of the silicon nitride of films 47 and 53 (sidewall spacer 48), for example. After this, the interlayer insulating film49 over the individual p-type semiconductor regions 9 and 9 (the sourceregions) of the load MISFETs Qp₁ and Qp₂ are opened to form connectionholes 50 and 50 by a dry-etching method using a photoresist as the mask.Simultaneously with this, the interlayer insulating film 49 over theindividual n-type semiconductor regions and (the source regions) of thedrive MISFETs Qd₁ and Qd₂ is opened to form connection holes 51 and 51,and the interlayer insulating film 49 over the individual n-typesemiconductor regions 5 and 5 (the other of the source region and thedrain region) of the transfer MISFETs Qt₁ and Qt₂ is opened to formconnection holes 52 and 52.

At the aforementioned step of forming the connection holes 50, 51 and 52by etching the interlayer insulating film 49 of PSG, due to the siliconnitride film 47 formed over the local wiring lines L₁ and L₂, and theside wall spacers of silicon nitride formed on the individual side wallsof the gate electrode 7 (the word line WL), the gate electrode 8 and thelocal wiring lines L₁ and L₂ are hardly etched because their etchingrates are different from (e.g., much less than) that of the material ofthe interlayer insulating film 49.

The connection holes 50, 51 and 52 and the local wiring lines L₁ and L₂can be positionally displaced due to the misregistration of thephotoresist mask used for forming the connection holes 50, 51 and 52 byetching the interlayer insulating film 49 and the photoresist mask usedfor forming the local wiring lines L₁ and L₂ by etching the TiN film.However, in the present embodiment, even with a partial overlap betweenany of the connection holes 50, 51 and 52 and the local wiring line L₁or the local wiring line L₂, neither the local wiring line L₁ nor thelocal wiring line L₂ is exposed from the side wall of any of theconnection holes 50, 51 and 52 when the interlayer insulating film 49 isetched, thereby preventing short circuit between the conductive film tobe deposited at a later step in the connection holes 50, 51 and 52 andthe local wiring line L₁ or the local wiring line L₂.

The connection holes 50 , 51 and 52, the gate electrode 7 (the word lineWL) and the gate electrode 8 can be relatively displaced due tomisregistration between the photoresist mask to be used for forming theconnection holes 50, 51 and 52 by etching the interlayer insulating film49 and the photoresist mask to be used for forming the gate electrode(the word line WL) and the gate electrode 8 by etching thepolycrystalline silicon film. However, in the present embodiment, evenwith a partial overlap between any of the connection holes 50, 51 and 52and the gate electrode 7 (the word line WL) or the gate electrode 8, thegate electrode 8 is not exposed from the side wall of the connectionhole 50 or 51, and the gate electrode 7 (the word line WL) is notexposed from the side wall of the connection hole 52 when the interlayerinsulating film 49 is etched, thereby preventing short circuit betweenthe conductive film to be deposited at a later step in the connectionholes 50, 51 and 52 and the gate electrode 7 (the word line WL) or thegate electrode 8.

In short, according to the manufacturing method of the presentembodiment, when the connection holes 50, 51 and 52 are laid out, it isunnecessary to take into consideration the registration allowancebetween the connection holes 50, 51 and 52 and the local wiring lines L₁and L₂ and the registration allowance between the connection holes 50,51 and 52 and the gate electrode 7 (the word line WL) and the gateelectrode 8. As a result, the connection holes 50, 51 and 52 can be laidout so as to be closer to the local wiring lines L₁ and L₂, the gateelectrode 7 (the word line WL) and the gate electrode 8 by a distancecorresponding to those registration allowances. Therefore, the areaoccupied by the memory cell can be reduced in both the first directionand the second direction perpendicular to the first direction.

In order that the side wall spacer 48 may function as the etchingstopper when the interlayer insulating film 49 is etched, the thicknessof the silicon nitride film 53 constituting the side wall spacer 48 hasto be larger than the registration allowance of the photoresist mask.The thickness of the silicon nitride film 53 is set to at least about200 nm when the sum of (1) the registration allowance between theconnection holes 50, 51 and 52 and the local wiring lines L₁ and L₂, and(2) the registration allowance between the connection holes 50, 51 and52 and the gate electrode 7 (the word line WL) and the gate electrode 8,is about 200 nm, for example.

Next, the thin silicon nitride film 13 at the bottoms of the connectionholes 50, 51 and 52 is etched. After this, as shown in FIGS. 61 and 62,power supply voltage line 22, reference voltage line 23 and anintermediate wiring line 54 are formed over the interlayer insulatingfilm 49. The power supply voltage line, reference voltage line andintermediate wiring line 22, 23 and 54 are formed by depositing aW-film, an Al film and a W-film consecutively over the interlayerinsulating film 49 by a sputtering method, and then by patterning thosefilms. Plugs of W-film may be formed, if necessary, in the connectionholes 50, 51 and 52.

Next, as shown in FIGS. 63 and 64, an interlayer insulating film 26 ofsilicon oxide is deposited by a CVD method over the power supply voltageline 22, the reference voltage line 23 and the intermediate wiring line54, and the interlayer insulating film 26 over the intermediate wiringline 54 is opened to form a connection hole 55 by a dry-etching methodusing a photoresist as the mask. After this, the data lines DL and DLare formed over the interlayer insulating film 26. These data lines DLand DL are formed by depositing a TiN film, an Al film and a TiN filmconsecutively over the interlayer insulating film 26 by sputtering andthen by patterning those films.

Embodiment 4

In the SRAM of the present embodiment, the paired local wiring lines L₁and L₂ are formed in the same conductive layer as in the SRAM of theforegoing embodiment 3. A method for manufacturing the memory cell ofthis SRAM will be described with reference to FIGS. 65 to 82.

First of all, as shown in FIGS. 65 and 66, a p-type well 3 and an n-typewell 4 are formed in the major face of a semiconductor substrate 1, anda field oxide film 28 for isolating the elements and a gate oxide film 6of an MISFET are then formed on those surfaces. After this, driveMISFETs Qd₁ and Qd₂ and transfer MISFETs Qt₁ and Qt₂ are formed in thep-type well 3, and load MISFETs Qp₁ and Qp₂ are formed in the n-typewell 4. A gate electrode 7 (the word line WL) of the transfer MISFETsQt₁ and Qt₂ and gate electrodes 8 and 8 of the drive MISFETs Qd₁ and Qd₂(the load MISFETs Qp₁ and Qp₂) are composed of a polycrystalline siliconfilm. The insulating films (the cap insulating films) covering the gateelectrode 7 (the word line WL) and the gate electrode 8 individually arecomposed of a silicon nitride film 56. This silicon nitride film 56 isdeposited thicker (the thickness is more than about 300 nm) than a laterdescribed silicon nitride film 13. Side wall spacers 11 on theindividual side walls of the gate electrode 7 (the word line WL) andgate electrode 8 are formed by etching a silicon oxide filmanisotropically.

Next, as shown in FIGS. 67 and 68, the silicon nitride film 56 over thegate electrode 8 of the drive MISFET Qd₁ (the load MISFET Qp₁) is etchedto form a connection hole 57, and the silicon nitride film 56 over thegate electrode 8 of the drive MISFET Qd₂ (the load MISFET Qp₂) is etchedto form a connection hole 58. The connection hole 57 is formed in theregion to be connected with the local wiring line L₂ at a later step,and the connection hole 58 is formed in the region to be connected withthe local wiring line L₁ at a later step.

Next, as shown in FIGS. 69 and 70, a Ti-silicide layer is formed on theindividual surfaces of the gate electrode 8 of the drive MISFET Qd₁ (theload MISFET Qp₁), exposed at the bottom of the connection hole 57, thegate electrode 8 of the drive MISFET Qd₂ (the load MISFET Qp₂), exposedat the bottom of the connection hole 58, n-type semiconductor regions 5and 5 (the source region and the drain region) of the transfer MISFETsQt₁ and Qt₂, the n-type semiconductor regions 5 and 5 (the source regionand the drain region) of the drive MISFETs Qd₁ and Qd₂, and p-typesemiconductor regions 9 and 9 (the source region and the drain region)of the load MISFETs Qp₁ and Qp₂.

In order to form the Ti-silicide layer 10, the gate oxide film 6,covering the surfaces of the individual n-type semiconductor regions 5and 5 (the source region and the drain region) of the drive MISFETs Qd₁and Qd₂ and transfer MISFETs Qt₁ and Qt₂, and the gate oxide film 6,covering the surface of the individual p-type semiconductor regions 5and 5 (the source region and the drain region) of the load MISFETs Qp₁and Qp₂, are etched. After this, a Ti-film is deposited over thesemiconductor substrate 1 by sputtering. Next, the semiconductorsubstrate 1 is annealed to cause reactions between the Ti-film and thesemiconductor substrate 1 (the n-type semiconductor region 5 and thep-type semiconductor region 9) and between the Ti-film and thepolycrystalline silicon film (the gate electrode 8 exposed at thebottoms of the connection holes 57 and 58), and the unreacted Ti-film isetched off.

Next, as shown in FIGS. 71 and 72, the silicon nitride film 13, as thinas about 30 nm, is deposited over the semiconductor substrate 1 by a CVDmethod. After this, the silicon nitride film 13 is dry-etched by using aphotoresist as the mask to form a connection hole 43, which reaches then-type semiconductor region 5 (the drain region) of the drive MISFET Qd₁and the gate electrode 8 of the drive MISFET Qd₂ (the load MISFET Qp₂),and a connection hole 44 which reaches the p-type semiconductor region 9(the drain region) of the load MISFET Qp₂ and the gate electrode 8 ofthe drive MISFET Qd₁ (the load MISFET Qp₁). Simultaneously with this, aconnection hole 45 is formed over the n-type semiconductor region 5 (thedrain region) of the drive MISFET Qd₂, and a connection hole 46 isformed over the p-type semiconductor region 9 (the drain region) of theload MISFET Qp₁.

Since a connection hole 58 is formed in advance over the gate electrode8 of the drive MISFET Qd₁ (the load MISFET Qp₁), the connection hole 43partially overlaps the connection hole 58 over the gate electrode 8.Likewise, since a connection hole 57 is formed in advance over the gateelectrode 8 of the drive MISFET Qd₂ (the load MISFET Qp₂), theconnection hole 44 partially overlaps the connection hole 57 over thegate electrode 8.

In short, by the manufacturing method of the present embodiment, whenthe connection holes 43, 44, 45 and 46 are laid out, it is unnecessaryto consider the registration allowance between those connection holes 43to 46 and the gate electrode 8 and the registration allowance betweenthe connection holes 43 to 46 and the connection holes 57 and 58. As aresult, the connection holes 43 to 46 can be laid out so as to be closerto the gate electrode 8 by a distance corresponding to thoseregistration allowances. Therefore the area occupied by the memory cellin the first direction can be reduced.

Specifically, even if the connection holes 43, 44, 45 and 46 overlap thegate electrode 8 when they are formed by etching the silicon nitridefilm 13, they do not reach the gate electrode 8 because the siliconnitride film 56, thicker than the silicon nitride film 13, is formedover the gate electrode 8. Since, moreover, there is a large differencein the etching rate between the silicon nitride film and the siliconoxide film, the side wall spacers 11, which are composed of the siliconoxide film on the individual side walls of the gate electrode 7 (or theword line WL) and the gate electrode 8, are hardly etched when thesilicon nitride film 13 is etched to form the connection holes 43, 44,45 and 46.

As a result, even if those connection holes 43 to 46 overlap the gateelectrode 8 when they are formed, the conductive film deposited in theconnection holes 43 to 46 and the gate electrode 8 do not short circuitat a later step.

Next, as shown in FIGS. 73 and 74, a TiN film having a thickness ofabout 100 nm is deposited over the silicon nitride film 13 by asputtering method or a CVD method, and a silicon nitride film 47 havinga thickness of about 100 nm is then deposited over that TiN film by aCVD method. After this, the silicon nitride film 47 and the TiN film arepatterned by a dry-etching method using a photoresist as the mask toform paired local wiring lines L₁ and L₂ composed of the TiN film.

The local wiring line L₁ is connected through the connection hole 43 andthe connection hole 58 with the gate electrode 8 of the drive MISFET Qd₂(the load MISFET Qp₂), through the connection hole 43 with the n-typesemiconductor region 5 (the drain region) of the drive MISFET Qd₁, andthrough the connection hole 46 with the p-type semiconductor region 9(the drain region) of the load MISFET Qp₁. The local wiring line L₂ isconnected through the connection hole 44 and the connection hole 57 withthe gate electrode 8 of the drive MISFET Qd₁ (the load MISFET Qp₁),through the connection hole 44 with the p-type semiconductor region 9(the drain region) of the load MISFET Qp₂, and through the connectionhole 45 with the n-type semiconductor region 5 (the drain region) of thedrive MISFET Qd₂.

The local wiring line L₁ is so arranged as to overlap with the gateelectrode 8 of the drive MISFET Qd₁ (the load MISFET Qp₁) and the gateelectrode 7 (the word line WL) of the transfer MISFETs Qt₁ and Qt₂, andthe local wiring line L₂ is so arranged as to overlap with the gateelectrode 8 of the drive MISFET Qd₂ (the load MISFET Qp₂) and the gateelectrode 7 (the word line WL) of the transfer MISFETs Qt₁ and Qt₂.Thanks to this construction, a capacitor element C' is formed of thelocal wiring line L₁, the gate electrode 8 and the silicon nitride film13 interposed therebetween, and a capacitor element C' is formed of thelocal wiring line L₂, the gate electrode 8 and the silicon nitride film13 interposed therebetween, so that the amount of charge of the storagenode can be increased to improve the alpha particle soft errorresistance of the memory cell.

Next, as shown in FIG. 75, a silicon nitride film 59 is deposited by aCVD method over the silicon nitride film 47 covering the local wiringlines L₁ and L₂, and an interlayer insulating film 49 of PSG isdeposited over the silicon nitride film 59 by the CVD method.

Next, as shown in FIG. 76 and 77, the interlayer insulating film 49 overthe individual p-type semiconductor regions 9 and 9 (the source regions)of the load MISFETs Qp₁ and Qp₂ are opened by a dry etching method usinga photoresist as the mask to form connection holes 50 and 50.Simultaneously with this, the interlayer insulating film 49 over theindividual n-type semiconductor regions 5 and 5 (the source regions) ofthe drive MISFETs Qd₁ and Qd₂ are opened to form connection holes 51 and51, and the interlayer insulating film 49 over the individual n-typesemiconductor regions 5 and 5 (the drain regions) of the transferMISFETs Qt₁ and Qt₂ are opened to form connection holes 52 and 52. Thisetching treatment is interrupted at the instant when the silicon nitridefilm 59 is exposed at the bottoms of the connection holes 50, 51 and 52.

Next, the etching gas for the silicon oxide is changed to that for thesilicon nitride, to etch the silicon nitride film 59 in the connectionholes 50, 51 and 52 and the thin silicon nitride film 13 below theformer, as shown in FIG. 78. This etching treatment is carried out inthe connection holes 50, 51 and 52 under the condition that the sidewall spacers are formed on the individual side walls of the gateelectrode 7 (the word line WL), the gate electrode 8 and the localwiring lines L₁ and L₂.

Thus, in the foregoing embodiment 3, the connection holes 50, 51 and 52are formed in the interlayer insulating film 49 after the side wallspacers 48 have been formed in advance on the individual side walls ofthe gate electrode 7 (the word line WL), the gate electrode 8 and thelocal wiring lines L₁ and L₂. In the present embodiment, on thecontrary, the side wall spacers of silicon nitride are formed when theconnection holes 50, 51 and 52 are formed by opening the interlayerinsulating film 49.

In this embodiment, like embodiment 3, the gate electrode 7 (the wordline WL), the gate electrode 8 and the local wiring lines L₁ and L₂ arenot exposed on the side walls of the connection holes 50, 51 and 52 evenif the connection holes 50, 51 and 52, the gate electrode 7 (the wordline WL), and the gate electrode 8 overlap with each other and theconnection holes 50, 51, and 52 and the local wiring lines overlap eachother due to the misregistration of the photoresist mask. In short, inthe case the manufacturing method of the present embodiment is used,when the connection holes 50, 51 and 52 are laid out, it is unnecessaryto take into consideration the registration allowance between theconnection holes 50, 51 and 52 and the local wiring lines L₁ and L₂ andthe registration allowance between the connection holes 50, 51 and 52and the gate electrode 7 (the word line WL) and the gate electrode 8. Asa result, the connection holes 50, 51 and 52 can be laid out so as to becloser to the local wiring lines L₁ and L₂, the gate electrode 7 (theword line WL) and the gate electrode 8 by a distance corresponding tothose registration allowances so that the area to be occupied by thememory cell can be reduced.

In order that the side wall spacers formed by the silicon nitride film59 may function as the etching stopper, the thickness of the siliconnitride film 59 is made larger than the registration allowance of theaforementioned photoresist mask.

Next, as shown in FIGS. 79 and 80, the power supply voltage line 22, thereference voltage line 23 and the intermediate wiring line 54 are formedover the interlayer insulating film 49 in accordance with themanufacturing method of the aforementioned embodiment 3. Next, as shownin FIGS. 81 and 82, the interlayer insulating film 26 is deposited overthe power supply voltage line 22, the reference voltage line 23 and theintermediate wiring line 54, and the interlayer insulating film 26 overthe intermediate wiring line 54 is opened to form the connection hole 55by a dry-etching method using a photoresist as the mask. After this, thedata lines DL and DL are 5 formed over the interlayer insulating film26.

According to the manufacturing method of the present embodiment, thereare required neither the registration allowance between the connectionholes 50, 51 and 52 and the local wiring lines L₁ and L₂ nor theregistration allowance between the connection holes 50, 51 and 52 andthe gate electrode 7 (the word line WL) and the gate electrode 8, andfurther neither the registration allowance between the connection holes43 and 44 and the gate electrode 8 nor the registration allowancebetween the connection hole 43 and the n-type semiconductor region 5(between the connection hole 44 and the p-type semiconductor region 9).As a result, the memory cell can be made smaller than that of theforegoing embodiment 3.

Embodiment 5

In the SRAM of the present embodiment, the paired local wiring lines L₁and L₂ are formed in different conductive layers, so that a capacitorelement C is formed of the upper local wiring line L₂, the lower localwiring line L₁ and a thin insulating film interposed therebetween. Themethod for manufacturing the memory cell of this SRAM will be describedwith reference to FIGS. 83, 84(a) and (b), 85, 86(a) and (b), 87, 88(a)and (b), 89, 90(a) and (b), 91(a) and (b), 92, 93(a) and (b), 94, 95(a)and (b), 96 and 97(a) and (b).

First of all, as shown in FIGS. 83 and 84(a) and (b), in accordance withthe manufacturing method of the foregoing embodiment 1, the elementisolating groove 2 and then the p-type well 3 and the n-type well 4 areformed in a major face of the semiconductor substrate 1, and the gateoxide film 6 of the MISFET is formed over the p-type well 3 and then-type well 4. After this, the drive MISFETs Qd₁ and Qd₂ and thetransfer MISFETs Qt₁ and Qt₂ are formed in the p-type well 3, and theload MISFETs Qp₁ and Qp₂ are formed in the n-type well 4. The gateelectrode 7 (the word line WL) and the gate electrode 8 are composed ofa polycrystalline silicon film, and the cap insulating film is composedof the silicon oxide film 12. The side wall spacers 11 on the individualside walls of the gate electrode 7 (the word line WL) and the gateelectrode 8 are formed by etching a silicon oxide film.

Next, as shown in FIGS. 85 and 86(a) and (b), in accordance with themanufacturing method of the foregoing embodiment 3, the Ti-silicidelayer 10 is formed to reduce the sheet resistance over the individualsurfaces of the gate electrode 7 (the word line WL) of the transferMISFETs Qt₁ and Qt₂, the gate electrode 8 and 8 of the drive MISFETs Qd₁and Qd₂ (the load MISFETs Qp₁ and Qp₂), the individual n-typesemiconductor regions 5 and 5 (the source region and the drain region)of the transfer MISFETs Qt₁ and Qt₂ and the drive MISFETs Qd₁ and Qd₂,the individual p-type semiconductor regions 9 and 9 (the source regionand the drain region) of the load MISFETs Qp₁ and Qp₂.

Next, as shown in FIGS. 87 and 88(a) and (b), the silicon nitride film13, deposited over the semiconductor substrate by a CVD method andhaving a small thickness of about 50 nm, is etched to form theconnection hole 14 over the gate electrode 8 of the drive MISFET Qd₂(the load MISFET Qp₂), the connection hole 40 over the n-typesemiconductor region 5 (the drain region) of the drive MISFET Qd₁ andthe connection hole 41 over the p-type semiconductor region 9 (the drainregion) of the load MISFET Qp₁. After this, the TiN film, deposited overthe silicon nitride film 13 by a sputtering method or a CVD method andhaving a thickness of about 100 nm, is patterned to form the localwiring line L₁. This local wiring line L₁ is given an area wide enoughto cover the six MISFETs constituting the memory cell. The local wiringline L₁ is connected through the connection hole 14 with the gateelectrode 8 of the drive MISFET Qd₂ (the load MISFET Qp₂), through theconnection hole 40 with the n-type semiconductor region 5 (the drainregion) of the drive MISFET Qd₁, and through the connection hole 41 withthe p-type semiconductor region 9 (the drain region) of the load MISFETQp₁.

Next, as shown in FIGS. 89 and 90(a) and (b), the silicon nitride film42, deposited over the semiconductor substrate 1 by a CVD method andhaving a small thickness of about 30 nm, is etched to form theconnection hole 18 over the gate electrode 8 of the drive MISFET Qd₁ (orthe load MISFET Qp₁), the connection hole 19 over the n-typesemiconductor region 5 (the drain region) of the drive MISFET Qd₂, andthe connection hole 20 over the p-type semiconductor region 9 (the drainregion) of the load MISFET Qp₂. After this the local wiring line L₂ of aTiN film is formed over the silicon nitride film 42. The local wiringline L₂ is connected through the connection hole 18 with the gateelectrode 8 of the drive MISFET Qd₁ (the load MISFET Qp₁), through theconnection hole 19 with the n-type semiconductor region 5 (the drainregion) of the drive MISFET Qd₂, and through the connection hole 20 withthe p-type semiconductor region 9 (the drain region) of the load MISFETQp₂.

The local wiring line L₂ is formed by depositing a TiN film having athickness of about 100 nm over the silicon nitride film 42 by asputtering method or a CVD method, by then depositing the siliconnitride film 47 having a thickness of about 100 nm over the TiN film bya CVD method, and thereafter by patterning the silicon nitride film 47and the TiN film by a dry etching method using a photoresist as themask. The local wiring line L₂ is given an area wide enough to cover thesix MISFETs constituting the memory cell and to overlap the lower localwiring line L₁ substantially completely in the region excepting the openregions of the connection holes 18, 19 and 20 and the registrationallowance region. As a result, the capacitor element C is formed of thelocal wiring lines L₁ and L₂ (the paired electrodes) and the siliconnitride film 42 (the dielectric film) made thinner than the local wiringlines L₁ and L₂. Moreover, the charge of the capacitor element C can beincreased so that the amount of stored charge of the storage node can beincreased to improve the alpha particle soft error resistance of thememory cell.

Next, as shown in FIG. 91(a) and (b), the side wall spacers 48 areformed on the individual side walls of the gate electrode 8, the lowerlocal wiring line L₁ and the upper local wiring line L₂. The side wallspacer 48 is also formed on the side wall of the gate electrode 7 (theword line WL), although not shown. The side wall spacers 48 are formedby etching a silicon nitride film which is deposited over the siliconnitride film 47 by a CVD method and has a thickness of about 200 nm.

Next, as shown in FIGS. 92 and 93(a) and (b), the interlayer insulatingfilm 49 of PSG having a thickness of about 400 nm is deposited over thesilicon nitride film 47 by a CVD method. After this, the interlayerinsulating film 49 is opened by a dry-etching method using a photoresistas the mask to form the connection holes 50 and 50 over the p-typesemiconductor regions 9 and 9 (the source regions) of the load MISFETsQp₁ and Qp₂, the connection holes 51 and 51 over the n-typesemiconductor region 5 and 5 (the source regions) of the drive MISFETsQd₁ and Qd₂, and the connection holes 52 and 52 over the n-typesemiconductor regions 5 and 5 (the drain regions) of the transferMISFETs Qt₁ and Qt₂. Since, at this time, the side wall spacers 48 onthe silicon nitride film act as the etching stoppers, neither the gateelectrode 8 is exposed at the side walls of the connection holes 50 and51, nor is exposed the gate electrode 7 (the word line WL) at the sidewall of the connection hole 52. Likewise, neither the lower local wiringline L₁ nor the upper local wiring line L₂ is exposed at the side wallsof the connection holes 50, 51 and 52.

In short, when the manufacturing method of the present embodiment isapplied to the SRAM in which the paired local wiring lines L₁ and L₂ arearranged in the different conductive layers, it is unnecessary to takeinto consideration the registration allowance between the connectionholes 50, 51 and 52 and the upper local wiring line L₂, and theregistration allowance between the connection holes 50, 51 and 52 andthe gate electrode 7 (the word line WL) and the gate electrode 8. As aresult, the connection holes 50, 51 and 52 can be so arranged as to becloser to the upper local wiring line L₂, the lower local wiring lineL₁, the gate electrode 7 (word line WL) and the gate electrode 8 by adistance corresponding to those registration allowances so that the areaoccupied by the memory cell can be reduced. In order that the side wallspacers 48 may function as the etching stoppers when the interlayerinsulating film 49 is etched, the thickness of the silicon nitride filmconstituting the side wall spacers 48 is made larger than theregistration allowance of the aforementioned photoresist mask.

In the present embodiment, the side wall spacers 48 of the siliconnitride are formed in advance on the individual side walls of the gateelectrode 7 (the word line WL), the gate electrode 8, the lower localwiring line L₁ and the upper local wiring line L₂, and the connectionholes 50, 51 and 52 are then formed in the interlayer insulating film49. As in the foregoing embodiment 4, the silicon nitride film and theinterlayer insulating film 49 are deposited over the silicon nitridefilm 47 covering the upper local wiring line L₂ so that the side wallspacers may be formed when the interlayer insulating film 49 is openedto form the connection holes 50, 51 and 52.

Next, as shown in FIGS. 94 and 95(a) and (b), in accordance with themanufacturing method of the foregoing embodiment 3, the power supplyvoltage line 22, the reference voltage line 23 and the intermediatewiring line 54 are formed over the interlayer insulating film 49. Afterthis, as shown in FIGS. 96 and 97(a) and (b), the interlayer insulatingfilm 26 is deposited over the power supply voltage line 22, thereference voltage line 23 and the intermediate wiring line 54, and theinterlayer insulating film 26 over the intermediate wiring line 54 isopened to form the connection hole 55. After this, the data lines DL andDL are formed over the interlayer insulating film 26.

According to the present embodiment, the paired local wiring lines L₁and L₂ are formed in different conductive layers and are so arranged asto be superposed on each other so that the area occupied by the memorycell can be reduced. At the same time, there are made unnecessary theregistration allowance between the connection holes 50, 51 and 52 andthe upper local wiring line L₂, the registration allowance between theconnection holes 50, 51 and 52 and the lower local wiring line L₁, andthe registration allowance between the connection holes 50, 51 and 52and the gate electrode 7 (the word line WL) and the gate electrode 8, sothat the area occupied by the memory cell can be further reduced.

According to the present embodiment, the upper local wiring line L₂ andthe lower local wiring line L1 are so arranged as to overlap with eachother over a wide area, and the capacitor element C is composed of thelocal wiring lines L₁ and L₂ and the thin insulating film interposedtherebetween, so that the alpha particle soft error resistance of thememory cell can be improved.

Embodiment 6

In the SRAM of the present embodiment, the paired local wiring lines L₁and L₂ are formed in different conductive layers, so that a capacitorelement C is formed of the upper local wiring line L₂, the lower localwiring line L₁ and a thin insulating film interposed therebetween. Themethod for manufacturing the memory cell of this SRAM will be describedwith reference to FIGS. 98, 99(a) and (b), 100, 101(a) and (b), 102,103(a) and (b), 104, 105(a) and (b), 106(a) and (b), 107(a) and (b), 108and 109.

First of all, as shown in FIGS. 98 and 99(a) and (b), in accordance withthe manufacturing method of the foregoing embodiment 1, the elementisolating groove 2 and then the p-type well 3 and the n-type well 4 areformed in a major face of the semiconductor substrate 1, and the gateoxide film 6 of the MISFET is formed over the p-type well 3 and then-type well 4. After this, the drive MISFETs Qd₁ and Qd₂ and thetransfer MISFETs Qt₁ and Qt₂ are formed in the p-type well 3, and theload MISFETs Qp₁ and Qp₂ are formed in the n-type well 4. The gateelectrode 7 (the word line WL) and the gate electrode 8 are composed ofa polycrystalline silicon 8a and Ti-silicide film 8b film, and the capinsulating film is composed of the silicon nitride film 12a. The sidewall spacers 11 on the individual side walls of the gate electrode 7(the word line WL) and the gate electrode 8 are formed byanisotropically etching a silicon nitride film which is deposited overthe gate electrodes 7, 8 and the cap insulating film 12a.

Next, as shown in FIGS. 100 and 101(a) and (b), in accordance with themanufacturing method of the foregoing embodiment 1, the Ti-silicidelayer 10 is formed to reduce the sheet resistance over the individualn-type semiconductor regions 5 and 5 (the source region and the drainregion) of the load MISFETs Qp₁ and Qp₂, and the individual p-typesemiconductor regions 9 and 9 (the source region and the drain region)of the load MISFETs Qp₁ and Qp₂.

Next, as shown in FIGS. 102 and 103(a) and (b), the silicon oxide film13a, deposited over the semiconductor substrate by a CVD method andhaving a small thickness of about 50 nm, is etched to form theconnection hole 14 over the gate electrode 8 of the drive MISFET Qd₂(the load MISFET Qp₂), the connection hole 40 over the n-typesemiconductor region 5 (the drain region) of the drive MISFET Qd₁ andthe connection hole 41 over the p-type semiconductor region 9 (the drainregion) of the load MISFET Qp₁. After this, a TiN film, deposited overthe silicon nitride film 13a by a sputtering method or a CVD method andhaving a thickness of about 100 nm, is patterned to form the localwiring line L₁. This local wiring line L₁ is given an area wide enoughto cover the six MISFETs constituting the memory cell. The local wiringline L₁ is connected through the connection hole 14 with the gateelectrode 8 of the drive MISFET Qd₂ (the load MISFET Qp₂), through theconnection hole 40 with the n-type semiconductor region 5 (the drainregion) of the drive MISFET Qd₁, and through the connection hole 41 withthe p-type semiconductor region 9 (the drain region) of the load MISFETQp₁.

Next, as shown in FIGS. 104 and 105(a) and (b), the silicon nitride film42, deposited over the semiconductor substrate 1 by a CVD method andhaving a small thickness of about 30 nm, is etched to form theconnection hole 18 over the gate electrode 8 of the drive MISFET Qd₁ (orthe load MISFET Qp₁), the connection hole 19 over the n-typesemiconductor region 5 (the drain region) of the drive MISFET Qd₂, andthe connection hole 20 over the p-type semiconductor region 9 (the drainregion) of the load MISFET Qp₂. After this the local wiring line L₂ of aTiN film is formed over the silicon nitride film 42. The local wiringline L₂ is connected through the connection hole 18 with the gateelectrode 8 of the drive MISFET Qd₁ (the load MISFET Qp₁), through theconnection hole 19 with the n-type semiconductor region 5 (the drainregion) of the drive MISFET Qd₂, and through the connection hole 20 withthe p-type semiconductor region 9 (the drain region) of the load MISFETQp₂.

The local wiring line L₂ is formed by depositing a TiN film having athickness of about 100 nm over the silicon nitride film 42 by asputtering method or a CVD method, by then depositing the siliconnitride film 47 having a thickness of about 100 nm over the TiN film bya CVD method, and thereafter by patterning the silicon nitride film 47and the TiN film by a dry etching method using a photoresist as themask. The local wiring line L₂ is given an area wide enough to cover thesix MISFETs constituting the memory cell and to overlap the lower localwiring line L₁ substantially completely in the region excepting the openregions of the connection holes 18, 19 and 20 and the registrationallowance region. As a result, the capacitor element C is formed of thelocal wiring lines L₁ and L₂ (the paired electrodes) and the siliconnitride film 42 (the dielectric film) made thinner than the local wiringlines L₁ and L₂. Moreover, the charge of the capacitor element C can beincreased so that the amount of stored charge of the storage node can beincreased to improve the alpha particle soft error resistance of thememory cell.

Next, as shown in FIG. 106(a) and (b), the side wall spacers 48a areformed on the individual side walls of the lower local wiring line L₁and the upper local wiring line L₂. The side wall spacer lla is alsoformed on the side wall of the gate electrode 7,8 (the word line WL).The side wall spacers 48a are formed by anisotropically etching asilicon nitride film which is deposited over the silicon nitride film 47by a CVD method and has a thickness of about 200 nm.

Next, as shown in FIGS. 107(a) and (b) and 108, the interlayerinsulating film 49 of PSG having a thickness of about 400 nm isdeposited over the silicon nitride film 47 by a CVD method. After this,the interlayer insulating film 49 is opened by a dry-etching methodusing a photoresist as the mask to form the connection holes 50 and 50over the p-type semiconductor regions 9 and 9 (the source regions) ofthe load MISFETs Qp₁ and Qp₂, the connection holes 51 and 51 over then-type semiconductor region 5 and 5 (the source regions) of the driveMISFETs Qd₁ and Qd₂, and the connection holes 52 and 52 over the n-typesemiconductor regions 5 and 5 (the drain regions) of the transferMISFETs Qt₁ and Qt₂. Since, at this time, the side wall spacers 48a, llaof the silicon nitride film and the silicon nitride film 47 act asetching stoppers, neither the gate electrode 8 is exposed at the sidewalls of the connection holes 50 and 51, nor is exposed the gateelectrode 7 (the word line WL) at the side wall of the connection hole52. Likewise, neither the lower local wiring line L₁ nor the upper localwiring line L₂ is exposed at the side walls of the connection holes 50,51 and 52.

In short, when the manufacturing method of the present embodiment isapplied to the SRAM in which the paired local wiring lines L₁ and L₂ arearranged in different conductive layers, it is unnecessary to take intoconsideration the registration allowance between the connection holes50, 51 and 52 and the upper local wiring line L₂, and the registrationallowance between the connection holes 50, 51 and 52 and the gateelectrode 7 (the word line WL) and the gate electrode 8. As a result,the connection holes 50, 51 and 52 can be so arranged as to be closer tothe upper local wiring line L₂, the lower local wiring line L₁, the gateelectrode 7 (word line WL) and the gate electrode 8 by a distancecorresponding to those registration allowances so that the area occupiedby the memory cell can be reduced. In order that the side wall spacers48a, 1la, and the silicon nitride film 47 may function as the etchingstoppers when the interlayer insulating film 49 is etched, the thicknessof the silicon nitride film constituting the side wall spacers 48a ismade larger than the registration allowance of the aforementionedphotoresist mask.

In the present embodiment, the side wall spacers 48a, lla of the siliconnitride are formed in advance on the individual side walls of the gateelectrode 7 (the word line WL), the gate electrode 8, the lower localwiring line L₁ and the upper local wiring line L₂, and the connectionholes 50, 51 and 52 are then formed in the interlayer insulating film49. As in the foregoing embodiment 4, the silicon nitride film and theinterlayer insulating film 49 can be deposited over the silicon nitridefilm 47 covering the upper local wiring line L₂ so that the side wallspacers may be formed when the interlayer insulating film 49 is openedto form the connection holes 50, 51 and 52.

Next, as shown in FIGS. 107(a) and (b) and 109, in accordance with themanufacturing method of the foregoing embodiment 3, the power supplyvoltage line 22, the reference voltage line 23 and the intermediatewiring line 54 are formed over the interlayer insulating film 49. Afterthis, as shown in FIGS. 96 and 97(a) and (b), the interlayer insulatingfilm 26 is deposited over the power supply voltage line 22, thereference voltage line 23 and the intermediate wiring line 54, and theinterlayer insulating film 26 over the intermediate wiring line 54 isopened to form the connection hole 55. After this, the data lines DL andDL are formed over the interlayer insulating film 26.

According to the present embodiment, the paired local wiring lines L₁and L₂ are formed in different conductive layers and are so arranged asto be superposed on each other so that the area occupied by the memorycell can be reduced. At the same time, there are made unnecessary theregistration allowance between the connection holes 50, 51 and 52 andthe upper local wiring line L₂, the registration allowance between theconnection holes 50, 51 and 52 and the lower local wiring line L₁, andthe registration allowance between the connection holes 50, 51 and 52and the gate electrode 7 (the word line WL) and the gate electrode 8, sothat the area occupied by the memory cell can be further reduced.

According to the present embodiment, the upper local wiring line L₂ andthe lower local wiring line L₁ are so arranged as to overlap with eachother over a wide area, and the capacitor element C is composed of thelocal wiring lines L₁ and L₂ and the thin insulating film interposedtherebetween, so that the alpha particle soft error resistance of thememory cell can be improved.

Although our invention has been specifically described in connectionwith its embodiments, it should not be limited thereto but can naturallybe modified in various manners without departing from the gist thereof.

The metal material of the local wiring lines can be selected from avariety of materials in addition to those of the foregoing embodiments.For example, the lower local wiring line may be made of a first-layeraluminum metal (TiN/Al/TiN) whereas the upper local wiring line may bemade of a second-layer aluminum metal. In this case, the power supplyvoltage line and the reference voltage line are made of a third layeraluminum metal whereas the complementary data lines are made of afourth-layer aluminum metal.

The effects obtained by the present invention disclosed herein will bebriefly described in the following.

According to the SRAM of the present invention, the paired local wiringlines cross-connecting the input/output terminals of the flip-flopcircuit of the memory cell are formed in different conductive layers. Asa result, the space, required to arrange the paired local wiring linestransversely when the two local wiring lines are composed of a commonconductive film, can be eliminated, so that the local wiring lines canbe so arranged as to overlap partially to reduce the area occupied bythe memory cell.

According to the SRAM of the present invention, the lower local wiringline and the upper local wiring line are so arranged as to overlap witheach other, and a capacitor element is composed of those local wiringlines and the insulating film interposed therebetween. As a result, thestorage node capacitance of the memory cell can be increased to preventa drop in the alpha particle soft error resistance which may be causedby the miniaturization of the memory cell size and the drop in theoperation power supply voltage.

According to the SRAM of the present invention, refractory metalsilicide layers of a low resistance material are formed on the surfacesof the source and drain regions of the drive MISFETs, the load MISFETsand the transfer MISFETs constituting the memory cell, so that thehigh-speed operation of the memory cell can be realized.

According to the SRAM of the present invention, the active region of thesemiconductor substrate (the p-type well) where the drive MISFETs andthe transfer MISFETs are formed, and the active region of thesemiconductor substrate (the n-type well) where the load MISFETs areformed, are isolated by the grooves which are opened in thesemiconductor substrate. As a result, the area occupied by the elementisolating region can be made lower than that of the case that theisolation is achieved by the field insulating film formed by a LOCOSmethod, so that the area occupied by the memory cell can be reduced.

According to the method for manufacturing the SRAM of the presentinvention, the mask registration allowance, when the connection holesare made in the interlayer insulating film by using a photoresist as themask, can be eliminated to reduce the area occupied by the memory cell.

While we have shown and described several embodiments in accordance withthe present invention, it is understood that the same is not limitedthereto, but is susceptible of numerous changes and modifications asknown to those skilled in the art. Therefore, we do not wish to belimited to the details shown and described herein, but intend to coverall such changes and modifications as are encompassed by the scope ofthe appended claims.

We claim:
 1. A semiconductor integrated circuit device, comprising anSRAM including memory cells each having a flip-flop circuit, eachflip-flop circut having a pair of drive MISFETs and a pair of loadMISFETs, each memory cell also including a pair of transfer MISFETs, thepair of drive MISFETs and the pair of load MISFETs forming a pair ofinverter circuits, the inverter circuits being cross-connected by firstand second local wiring lines, wherein gate electrodes of each of thedrive MISFETs and the load MISFETs are formed from a first layer ofconductive material overlying a semiconductor substrate, the first localwiring line is formed from a second layer of conductive material furtherfrom the substrate than said first layer of conductive material, and thesecond local wiring line is formed from a third layer of conductivematerial further from the substrate than said second layer of conductivematerial.
 2. A semiconductor integrated circuit device as set forth inclaim 1, wherein the first local wiring line and the second local wiringline are positioned so as to at least partially overlap each other, andare spaced from each other in a direction extending away from thesemiconductor substrate so as to form a space therebetween, and whereinthe device further includes an insulating film in the space between thefirst and second local wiring lines, so as to form a capacitor elementfrom the first and second local wiring lines and the insulating film. 3.A semiconductor integrated circuit device as set forth in claim 2,wherein the first and second local wiring lines overlap each other inregions other than open regions above connection holes, through whichthe second local wiring line and the MISFETs providing said flip-flopcircuit are connected, and registration allowance regions of saidconnection holes.
 4. A semiconductor integrated circuit device as setforth in claim 2, wherein said insulating film interposed between saidone and other local wiring lines is a silicon nitride film or a tantalumpentoxide film.
 5. A semiconductor integrated circuit device as setforth in claim 4, wherein said second conductive film and said thirdconductive film are individually made of a metal material.
 6. Asemiconductor integrated circuit device as set forth in claim 5, whereinat least said second conductive film, of said second conductive film andsaid third conductive film, is made of a refractory metal or compoundthereof.
 7. A semiconductor integrated circuit device as set forth inclaim 5, wherein at least said third conductive film, of said secondconductive film and said third conductive film, is made of a metalmaterial containing aluminum.
 8. A semiconductor integrated circuitdevice as set forth in claim 3, wherein said second conductive film andsaid third conductive film are individually made of a metal material. 9.A semiconductor integrated circuit device as set forth in claim 2,wherein said second conductive film and said third conductive film areindividually made of a metal material.
 10. A semiconductor integratedcircuit device as set forth in claim 2, wherein the first local wiringline and the second local wiring line are individually located overlyingthe gate electrodes and drain regions of said drive MISFETs, the gateelectrodes and drain regions of said load MISFETs and gate electrodes ofsaid transfer MISFETs.
 11. A semiconductor integrated circuit device asset forth in claim 1, wherein a refractory metal silicide layer isformed over surfaces of individual source regions and drain regions ofsaid drive MISFETs, said load MISFETs and said transfer MISFETs.
 12. Asemiconductor integrated circuit device as set forth in claim 1, whereina refractory metal silicide layer is formed over surfaces of individualgate electrodes and individual source regions and drain regions of saiddrive MISFETs, said load MISFETs and said transfer MISFETs.
 13. Asemiconductor integrated circuit device as set forth in claim 1, furthercomprising a reference voltage line connected with individual sourceregions of said drive MISFETs, a power supply voltage line connectedwith individual source regions of said load MISFETs, and data linesconnected to individual drain regions of said transfer MISFETs, saidreference voltage line and said power supply voltage line being formedfrom a fourth conductive film further from the substrate than said thirdconductive film, and said data lines being formed from a fifthconductive film further from said substrate than said fourth conductivefilm.
 14. A semiconductor integrated circuit device as set forth inclaim 1, wherein the drive MISFETs and the transfer MISFETs are locatedin a first conductivity type active region of the semiconductorsubstrate, and the load MISFETs are located in a second conductivitytype active region of the semiconductor substrate, and wherein a grooveis provided in the semiconductor substrate between the firstconductivity type active region and the second conductivity type activeregion so as to isolate the first conductivity type active region fromthe second conductivity type active region.
 15. A semiconductorintegrated circuit device as set forth in claim 14, wherein the firstconductivity type in opposite to the second conductivity type.
 16. Asemiconductor integrated circuit device as set forth in claim 1, whereinsaid second conductive film and said third conductive film areindividually made of a metal material.
 17. A semiconductor integratedcircuit device set forth in claim 1, wherein gate electrodes of thetransfer MISFETs are also formed from said first layer of conductivematerial.
 18. A semiconductor integrated circuit device according toclaim 1, wherein the first and second local wiring lines overlap eachother in regions other than open regions above connection holes, throughwhich the second local wiring line and the MISFETs providing saidflip-flop circuit are connected, and other than registration allowanceregions of said connection holes.
 19. A semiconductor integrated circuitdevice according to claim 1, wherein the first local wiring line and thesecond local wiring line are individually located overlying the gateelectrodes and drain regions of said driver MISFETs, the gate electrodesand drain regions of said load MISFETs and gate electrodes of saidtransfer MISFETs.
 20. A semiconductor integrated circuit device,comprising an SRAM including memory cells each having a flip-flopcircuit, each flip-flop circuit having a pair of driver MISFETs and apair of load MISFETs, each memory cell also including a pair of transferMISFETS, gate electrodes of each of the drive MISFETs, load MISFETs andtransfer MISFETs being formed from a first layer of conductive materialoverlying a semiconductor substrate, said gate electrodes having gateelectrode side wall spacers on side walls thereof, made of a firstinsulating material, the pair of drive MISFETs and the pair of loadMISFETs forming a pair of inverter circuits;first and second localwiring lines respectively cross-connecting the inverter circuits, sidewalls of the first and second local wiring lines having local wiringline side wall spacers thereon, the local wiring line side wall spacersbeing made of a second insulating material; a layer of a thirdinsulating material overlying the first and second local wiring lines,the layer of the third insulating material having connection holestherethrough for connection of wiring thereabove to source or drainregions of the drive MISFETs, load MISFETs and transfer MISFETs, whereinthe third insulating material is a material having a higher rate ofetching than does the first and second insulating materials.
 21. Thesemiconductor integrated circuit device as set forth in claim 20,wherein the side walls of the first and second local wiring linesoverlies the gate electrodes.
 22. The semiconductor integrated circuitdevice as set forth in claim 21, wherein local wiring line side wallspacers and gate electrode side wall form a single side wall spacerextending continuously on side walls of a respective a local wiring lineand a respective gate electrode.
 23. The semiconductor integratedcircuit device as set forth in claim 20, wherein the local wiring lineside wall spacers and the gate electrode side wall spacers areindividual side wall spacers.
 24. The semiconductor integrated circuitdevice as set forth in claim 20, wherein the first and second localwiring lines overlap each other, and wherein the device further includesa dielectric film between the first and second local wiring lines wherethe local wiring lines overlap, the first and second local wiring linesand the dielectric film therebetween forming a capacitor element. 25.The semiconductor integrated circuit device as set forth in claim 20,further comprising a power supply voltage line and a reference voltageline each overlying the third insulating film, a fourth insulating filmoverlying the power supply voltage line and the reference voltage line,and data lines overlying the fourth insulating film.
 26. Thesemiconductor integrated circuit device as set forth in claim 25,further comprising intermediate interconnect lines overlying the thirdinsulating film, connected to source or drain regions of the transferMISFETs, the intermediate interconnect lines being connected to the datalines overlying the fourth insulating films through holes in the fourthinsulating film, the intermediate interconnect lines being connected tothe source or drain regions of the transfer MISFETs through holes in thethird insulating film.
 27. A semiconductor integrated circuit devicecomprising an SRAM including memory cells having a flip-flop circuitcontaining a pair of drive MISFETs and a pair of load MISFETs,manufactured by a method comprising the steps of:(a) providing asemiconductor substrate having a major face, over which individual gateelectrodes of said drive MISFETs and said load MISFETs are formed; (b)forming at least one of a pair of local wiring lines, to cross-connect apair of input-output terminals of said flip-flop circuit, extendingfurther from said substrate than said gate electrodes; (c) forming sidewall spacers on individual side walls of at least one of (i) said gateelectrodes and (ii) said at least one of a pair of local wiring lines,by depositing a first insulating film over said at least one of the pairof local wiring lines and etching the first insulating film; and (d)forming connection holes reaching source regions of said drive MISFETsor said load MISFETS, by depositing a second insulating film having anetching rate greater than that of said first insulating film, over theat least one of the pair of local wiring lines, and by etching saidsecond insulating film.
 28. A semiconductor integrated circuit devicecomprising an SRAM including memory cells having a flip-flop circuitcontaining a pair of drive MISFETs and a pair of load MISFETs,manufactured by a method comprising the steps of:(a) providing asemiconductor substrate having a major face, over which individual gateelectrodes of said drive MISFETs and said load MISFETs are formed; (b)forming both of a pair of local wiring lines, to cross-connect a pair ofinput/output terminals of said flip-flop circuit, overlying said gateelectrodes; (c) forming side wall spacers on individual side walls of atleast one of (i) said gate electrodes and (ii) said both of the pair oflocal wiring lines, by depositing a first insulating film over said bothof the pair of local wiring lines and etching the first insulating film;and (d) forming connection holes reaching source regions of said driveMISFETs or said load MISFETs, by depositing a second insulating filmhaving an etching rate greater than that of said first insulating film,over the both of the pair of local wiring lines, and by etching saidsecond insulating film, and wherein a dielectric film is providedbetween the gate electrodes and the pair of local wiring lines, so as toform capacitor elements between the gate electrodes and local wiringlines.